Dr. Musaida Mercy Manyuchi is a professional Chemical Engineer by training and holds a Doctor of Technology in Chemical Engineering from Cape Peninsula University of Technology in South Africa, a Master of Science in Engineering Degree from Stellenbosch University in South Africa and a Bachelor of Engineering Honours in Chemical Engineering from the National University of Science and Technology in Zimbabwe. Dr. Mercy Manyuchi is a Research Fellow with the BioEnergy and Environmental Technology Centre in the Faculty of Engineering and the Built Environment at the University of Johannesburg. She is also a Faculty Member for the Chemical and Processing Engineering Department at the Manicaland State University of Applied Sciences in Zimbabwe. Dr. Manyuchi was also a Faculty Member in the Chemical and Process Systems Engineering Department at the Harare Institute of Technology in Zimbabwe where she also served as the Head of Department for 5 years. Dr. Manyuchi was also a Visiting Research Scholar at the German Biomass Research Institute in Germany. Dr. Manyuchi is a professional member of the Engineering Council of South Africa, South Africa Institute of Chemical Engineers, Engineering Council of Zimbabwe, Zimbabwe Institute of Engineers and the World Federation of Engineering Organizations.Dr. Manyuchi’s research interest lies in Waste to Energy Technologies and the Value Addition of Waste to Bio Products. To date she has published more than 30 research articles in peer reviewed journals and conferences, 2 books and 5 book chapters in the waste valorisation area. Dr. Manyuchi’s work in green initiatives has won several awards including the prestigious German based Green Talents, the SanBioFemBiz, the Research Council of Zimbabwe Outstanding Research Award, the Japanese International Award for Young Researchers and Africa Award for AgriTech Innovators.
Huge amounts of organic waste are being generated on a daily basis. This waste has potential to b... more Huge amounts of organic waste are being generated on a daily basis. This waste has potential to be converted to bio char through the pyrolysis technology and can act as bio adsorbent and bio filter during wastewater treatment. In this study, municipal wastewater was treated with bio char at the bio filtration stage and the changes in the chemical oxygen demand (COD), total suspended solids (TSS), total Kjeldahl nitrogen (TKN), total phosphates (TP) and pH were measured before and after treatment with biochar using standard methods. Bio char with surface area of 1000 m 2 /g and loading of 1 g/L was steam activated was used. The wastewater COD, TSS, TKN and TP showed a 90%, 89%, 64% and 78% reduction respectively after being passed through the bio char bio filter. In addition the wastewater pH changed from alkaline to neutral. Bio char can be effectively be used as a bio filter in wastewater treatment to meet guidelines for wastewater effluent disposal.
This study investigates the potentially of biologically treating opaque beer wastewater using
the... more This study investigates the potentially of biologically treating opaque beer wastewater using the bio augmentation technology at the same time harnessing biogas and bio solids as value added products. Wastewater sample were collected in 5L containers and the sludge was separated from the liquid. The liquid and sludge were bio augmented with Acti-zyme with loadings of 5g/L, 10g/L and 15 g/L and were left to settle over a period of 30 days under anaerobic conditions. The wastewater and treated effluent BOD, COD, TKN, TP, TSS, TDS and pH were measured using standard methods. Whereas the amount of biogas generated was measured using the water displacement and its composition quantified. The BOD, COD, TKN, TP, TSS, TDS were significantly reduced by 93%, 77%, 87%, 89%, 90% and 90% respectively. The BOD/COD ratio was 0.72 initially and reduced to 0.21 for all the Actizyme loadings. Biogas with a methane composition of 65-70% was recovered.
In this study, corn sillage was converted to vermicompost and vermiwash through earthworm bio con... more In this study, corn sillage was converted to vermicompost and vermiwash through earthworm bio conversion. Eisenia Fetida earthworms loaded at a rate of 2.5 kg/m 2 were used as the vermicomposting media over a period of 30 days in a vermireactor. The corn sillage vermiwash and vermicompost produced were analysed for bio fertilizer nutritional composition. The vermicompost had a nitrogen, phosphorous and potassium (NPK) composition of 0.52-1.53%, 0.18-1.06% and 0.13-0.74% respectively, whilst the vermiwash had an NPK composition of 0.011-1.83%, 0.003-1.65% and 0.062-1.73% respectively. Bio conversion of corn sillage to vermi-products presents an opportunity to boost food security and at the same time resource recovery from waste.
In the present study, the potential to produce bio pellets from organic landfill waste was invest... more In the present study, the potential to produce bio pellets from organic landfill waste was investigated as a strategy to promote sustainability of landfills as well as provision of alternative clean energy source. Organic waste was first shredded then compacted to pellets. Afterwards, the pellets went through carbonization at 400 °C for 30 minutes. The organic waste and bio pellets moisture content, ash content, volatile matter, fixed carbon and calorific value were measure. The calorific value of the bio pellets was 50% higher in comparison to the organic waste. The organic waste carbonization also resulted in a 97% increase in the fixed carbon content, 50% decrease in ash and volatile content matter as well as 86% decrease in moisture content. Landfill organic waste can be converted to form bio pellets with characteristics identical to coal.
In this study, activated biochar from municipal sewage sludge was used for the treatment of sewag... more In this study, activated biochar from municipal sewage sludge was used for the treatment of sewage wastewater. The sewage physicochemical parameters were measured before and after bio filtration with biochar applying the principle of adsorption using the standard methods. Bio char with 500 m 2 /g surface area and particle size of 0.5-1.0 mm was used at a loading rate of 2.5 g/L and treatment time of 40 hours. The changes in the sewage physicochemical parameters which included biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphates (TP), total solids (TS) and total Kjeldahl nitrogen (TKN) and were measured using standard methods. Upon subjecting the sewage water to the bio char, a reduction of 94%, 90%, 80%, 83% and 82% were observed for the BOD, COD, TP, TS and TKN respectively. The sewage pH also changed from alkaline to neutral. The observed results indicated that sewage sludge bio char can effectively treat sewage wastewater.
In this study, an assessment of the available sources of biomass and the associated technologies ... more In this study, an assessment of the available sources of biomass and the associated technologies are given for possible energy efficiency improvement. Bio char, a by product of biomass carbonization was assessed as a potential soil amendment as well as nutrient cycle agent. Bio energy is 80% efficient and if sustainable technologies are adopted the value can be increased so that the bio char available also increases. Usage of bio char in soil amendment improves the soil moisture content and has potential to act as a liming agent. High crop yields of up to 140% have been reported upon bio char use with application rates of at least 10 tons/hectare in field crops. The behaviour is attributed to the Terra preta effect caused by bio char and also increased micro organisms' habitants in the soil. However, several gaps such as the effect of carbonization temperature, source of biomass and its loading and their effects on nutrient cycling on the soil and plants still need to be understand in order to improve the nutrient cycling effects as well as the biomass cycle.
Tea wastes are generated on a daily basis in tea estates and these pose an environmental threat d... more Tea wastes are generated on a daily basis in tea estates and these pose an environmental threat due to greenhouse gases emissions yet these presents an opportunity of generation of biomass briquettes. In this study, tea wastes were converted to bio char at 300°C and ground to a particle size of less than 8mm. The bio char was compacted to form briquettes with a calorific value of 22-24 MJ/kg and moisture content of less than 10%. The tea waste briquettes can be integrated back into the tea manufacturing system as a co firing agent with coal or as an independent energy generator.
This study focused on the investigation of bio treatment of brewery wastewater using engineered m... more This study focused on the investigation of bio treatment of brewery wastewater using engineered micro organisms like Hycura. Brewery wastewater was treated in a 10L tank over a 5 day period with Hycura loadings of 0.05 g/L. The wastewater chemical oxygen demand (COD), biological oxygen demand (BOD), pH, total suspended solids (TSS), total Kjeldahl nitrogen (TKN) and total phosphates (TP) were measured using standard methods on a daily basis. The ph of the brewery waste changed from alkaline to neutral during the treatment process whilst the COD reduced by 87%, BOD by 88%, TSS by 94%, TKN by 68% and TP by 81%. The effective bio treatment of the brewery wastewater is attributed to the metabolism of Hycura.
The production of alternative energy sources from waste residues is increasingly becoming popular... more The production of alternative energy sources from waste residues is increasingly becoming popular. This paper focuses on the value addition of brewery spent grains waste by converting it to bio coal using hydrothermal carbonization. Brewery spent grains (BSG) from a local brewery company were used to determine the potential of making bio coal that can be used as a replacement to the conventional fossil fuel. Hydrothermal carbonization was conducted at 200 °C at a pressure of 25 bars for a residence time of 2 hours. The BSG were mixed with wastewater in the ratio 5:1. The bio coal that was produced had a calorific value of 26.1 MJ/kg and a fixed carbon content of 53.1%. The calorific values and fixed carbon were slightly higher than the conventional fossil coal which is an indication than BSG provides an alternative source of raw material for bio coal production, a source of renewable energy.
Due to waster scarcity, several cheap and user friendly technologies are being adopted to improve... more Due to waster scarcity, several cheap and user friendly technologies are being adopted to improve the efficiency in operation of wastewater treatment plants. In this study, Hycura, an engineered biocatalyst is proposed for use as a bio nutrient removal catalyst in municipal wastewater in a bid to enhance the treatment methods and improve the quality of effluent being disposed. The effectiveness of bio nutrient removal was measured through the biological oxygen demand (BOD), the chemical oxygen demand (COD), the total Kjeldahl nitrogen (TKN) and the total phosphates (TP) ratios. The COD/BOD ratios were >1.25, whilst the BOD/TKN ratios were >4.2, the COD/TKN ratios were >8.0 and the COD/TP ratios were >15. The ratios indicated a high bio degradability of bio nutrients from the municipal wastewater enhancing bio contaminants removal upon addition of Hycura to the system.
In this study, the potential to generate electricity from sewage sludge biogas harnessed from mun... more In this study, the potential to generate electricity from sewage sludge biogas harnessed from municipal sewage plants was investigated. Two sewage plants Crow borough and Marlborough were investigated as the potential raw material suppliers for the biogas generation. Sewage sludge samples were collected sand analyses for the total solids (TS), volatile solids (VS) and chemical oxygen demand (COD) among other parameters. Biogas generation was quantified in 250 mL flasks conducted under anaerobic conditions at mesophilic temperatures of 37 °C and thermophilic temperatures of 55 °C and agitation rates of 200 rpm. Optimum biogas production was achieved at 37 °C and 200 rpm with a methane composition of 72% before upgrading. The sewage sludge digestion to biogas was confirmed by the decrease in both TS and VS by 25.4% and 14.5% respectively. The average biogas generation rate was 0.015 m 3 /L with a Wobbe index of 24.78 indicating the high calorific value of the biogas and its potential to be generated to electricity.
In this study, the co-briquetting of coal fines saw dust and molasses as a binder is explored as ... more In this study, the co-briquetting of coal fines saw dust and molasses as a binder is explored as an option for value addition of the wastes generated in the various industries. The effect of the saw dust concentration and the molasses concentration was investigated through measuring the briquette's calorific value, fixed carbon, com-pressive strength and shatter index. Addition of Ca(OH) 2 was done to effect removal of sulphur from the bri-quette. Measurements of the briquettes physicochemical properties such as moisture content, ash content and sulphur content were measured using the standard methods. As the saw dust and the molasses concentration increased, the calorific value, fixed carbon and compressive strength increased by 16%, 8% and 50% respectively. Whereas, the shatter index decreased by 146% as the saw dust and the molasses concentration increased in relation to the coal fines. Addition of the saw dust and the molasses are therefore critical in the production of a high quality coal-saw dust-molasses briquette which does not shatter.
In this study, paper mill sludge was converted to biochar using the pyrolysis technology for appl... more In this study, paper mill sludge was converted to biochar using the pyrolysis technology for application in wastewater treatment. Paper mill sludge was pyrolyzed at 400-1000°C at a heating rate of 10°C/minute and carbonizing time of 45 minutes in a lab scale pyrolysis reactor. The biochar was ground to particle size of 1.8 mm and surface area of 500 m2/g and activated using steam. The paper mill biochar was loaded in a lab made adsorption column with a radius of 1.5 cm and length of 20 cm at a loading of 0.02 g/cm3 and used for treatment of textile wastewater as a bio-adsorbent. The change in the textile wastewater total dissolved solids (TDS), total suspended solids (TSS) and chemical oxygen demand (COD). The optimal adsorption time was 15 seconds, and this resulted in increased absorbance and transmittance in the treated effluent. Furthermore, the treated effluent TDS, TSS and COD significantly reduced by more than 97% upon using the paper mill biochar as an adsorbent. After consideration of a textile wastewater treatment plant treating 263 mega liters of wastewater per annum, a total capital investment of $ 67800 is required for the modified adsorption process with biochar costing $30/kg. The return on investment was found to be 52% with a payback period of 1.9 years. Profit will start to be realized after treating 140000 m3 of textile wastewater.
In this present study, Jatropha Carcus cake, a by product from the bio diesel production process ... more In this present study, Jatropha Carcus cake, a by product from the bio diesel production process was destabilization through vermicomposting to produce bio fertilizers. Jatropha Curcas cake was vermicomposted over a period 30 days using Eisenia Fetida earthworms. The nitrogen, phosphorous and potassium (NPK) content in the cake was continuously monitored using AOAC methods and the same was done for the leachate (vermiwash) produced during the vermicomposting process. The NPK content in the Jatropha Curcas cake increased with increase in the vermicomposting period with a 35% increase in N, 58% increase in P and a 98% increase in K. Furthermore, the vermiwash produced had an NPK with a composition of 2.1%, 0.75% and 0.51% respectively. The bio stabilization of the Jatropha Curcas cake through vermicomposting to bio fertilizers.
The brewery industry is one of the major industries in Zimbabwe and the following study was condu... more The brewery industry is one of the major industries in Zimbabwe and the following study was conducted to assess the techno-economic feasibility of reuse of wastewater after treatment using the biofilm that forms on the bio carriers. The malting plant of a certain brewing plant uses up to 350000 cubic meters water a year discharging about 75% of the biologically contaminated water as effluent which is discharged into the ecosystem. A biological water treatment approach was done using a moving bed biofilm reactor, with use of Mutag biochips. The treatment resulted in 93% BOD reduction, 87.9% COD reduction, 48% TSS reduction, 44% TDS reduction and a 97.8% increase in DO at a treatment period of 24 hours. An economic analysis was done with a payback period of 2.09 years and return on investment of 49% indicating the techno-economic viability of brewery wastewater.
This study investigated the potential to harvest biogas from tea waste as a resource recovery and... more This study investigated the potential to harvest biogas from tea waste as a resource recovery and waste management initiative. The tea waste was shredded to a particle size of less than 2.5 mm and anaerobically digested over a period of 30 days in 10-L digesters. The composition of biogas obtained was 60% to 65% methane with a yield of 0.2 L/g of tea waste feedstock. A reduction in the tea waste chemical oxygen demand and volatile solids composition by more than 50% indicated that optimal tea waste digestion had occurred. The tea waste digestate was rich in nitrogen (4.5%), phosphorous (0.6%), and potassium (4.6%) and could potentially be adopted as a biofertilizer. Biogas and biosolids can be generated from tea waste as a waste to resource initiative.
The potential to produce biogas and bio hydrogen from corn residue was investigated. A sample of ... more The potential to produce biogas and bio hydrogen from corn residue was investigated. A sample of 10g initially hydrothermally treated to liberate the cellulose and hemicellulose rich hydrolysate. Three steps for treatment at 80 • C for 15 min; 180 • C for 40 min and 190 • C and 10 min were investigated for corn residue conversion to soluble sugars. The highest cellulose yield was 0.356g per gram of corn residues through fermentation and 0.312g of bio hydrogen per gram of corn residues. An industrial process for the co-generation of biogas and bio-hydrogen from corn stover was then proposed from the experimental work.
Landfill organic waste fraction was investigated for the potential to generate bio ethanol, a liq... more Landfill organic waste fraction was investigated for the potential to generate bio ethanol, a liquid bio fuel that can be used in place of the conventional liquid fuels. This was achieved through acid treatment enzymatic hydrolysis. The organic fraction waste was first pre-treated with dilute sulphuric acid at 121 °C for 15 minutes. Afterwards it underwent enzymatic hydrolysis at 50 °C for a period of 5 days to allow the release of C6 sugars. The hydrolysate was then fermented at 30 °C for 5 days with yeast inoculated as the bio catalyst to produce bio ethanol. Enzymatic hydrolysis and the prior pre-treatment resulted in a high yield of 60% of the C6 sugars. The bio ethanol produced from the fermentable sugars was 40%. There is potential for utilization of the organic municipal waste fraction for bio fuels production.
Huge amounts of organic waste are being generated on a daily basis. This waste has potential to b... more Huge amounts of organic waste are being generated on a daily basis. This waste has potential to be converted to bio char through the pyrolysis technology and can act as bio adsorbent and bio filter during wastewater treatment. In this study, municipal wastewater was treated with bio char at the bio filtration stage and the changes in the chemical oxygen demand (COD), total suspended solids (TSS), total Kjeldahl nitrogen (TKN), total phosphates (TP) and pH were measured before and after treatment with biochar using standard methods. Bio char with surface area of 1000 m 2 /g and loading of 1 g/L was steam activated was used. The wastewater COD, TSS, TKN and TP showed a 90%, 89%, 64% and 78% reduction respectively after being passed through the bio char bio filter. In addition the wastewater pH changed from alkaline to neutral. Bio char can be effectively be used as a bio filter in wastewater treatment to meet guidelines for wastewater effluent disposal.
This study investigates the potentially of biologically treating opaque beer wastewater using
the... more This study investigates the potentially of biologically treating opaque beer wastewater using the bio augmentation technology at the same time harnessing biogas and bio solids as value added products. Wastewater sample were collected in 5L containers and the sludge was separated from the liquid. The liquid and sludge were bio augmented with Acti-zyme with loadings of 5g/L, 10g/L and 15 g/L and were left to settle over a period of 30 days under anaerobic conditions. The wastewater and treated effluent BOD, COD, TKN, TP, TSS, TDS and pH were measured using standard methods. Whereas the amount of biogas generated was measured using the water displacement and its composition quantified. The BOD, COD, TKN, TP, TSS, TDS were significantly reduced by 93%, 77%, 87%, 89%, 90% and 90% respectively. The BOD/COD ratio was 0.72 initially and reduced to 0.21 for all the Actizyme loadings. Biogas with a methane composition of 65-70% was recovered.
In this study, corn sillage was converted to vermicompost and vermiwash through earthworm bio con... more In this study, corn sillage was converted to vermicompost and vermiwash through earthworm bio conversion. Eisenia Fetida earthworms loaded at a rate of 2.5 kg/m 2 were used as the vermicomposting media over a period of 30 days in a vermireactor. The corn sillage vermiwash and vermicompost produced were analysed for bio fertilizer nutritional composition. The vermicompost had a nitrogen, phosphorous and potassium (NPK) composition of 0.52-1.53%, 0.18-1.06% and 0.13-0.74% respectively, whilst the vermiwash had an NPK composition of 0.011-1.83%, 0.003-1.65% and 0.062-1.73% respectively. Bio conversion of corn sillage to vermi-products presents an opportunity to boost food security and at the same time resource recovery from waste.
In the present study, the potential to produce bio pellets from organic landfill waste was invest... more In the present study, the potential to produce bio pellets from organic landfill waste was investigated as a strategy to promote sustainability of landfills as well as provision of alternative clean energy source. Organic waste was first shredded then compacted to pellets. Afterwards, the pellets went through carbonization at 400 °C for 30 minutes. The organic waste and bio pellets moisture content, ash content, volatile matter, fixed carbon and calorific value were measure. The calorific value of the bio pellets was 50% higher in comparison to the organic waste. The organic waste carbonization also resulted in a 97% increase in the fixed carbon content, 50% decrease in ash and volatile content matter as well as 86% decrease in moisture content. Landfill organic waste can be converted to form bio pellets with characteristics identical to coal.
In this study, activated biochar from municipal sewage sludge was used for the treatment of sewag... more In this study, activated biochar from municipal sewage sludge was used for the treatment of sewage wastewater. The sewage physicochemical parameters were measured before and after bio filtration with biochar applying the principle of adsorption using the standard methods. Bio char with 500 m 2 /g surface area and particle size of 0.5-1.0 mm was used at a loading rate of 2.5 g/L and treatment time of 40 hours. The changes in the sewage physicochemical parameters which included biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphates (TP), total solids (TS) and total Kjeldahl nitrogen (TKN) and were measured using standard methods. Upon subjecting the sewage water to the bio char, a reduction of 94%, 90%, 80%, 83% and 82% were observed for the BOD, COD, TP, TS and TKN respectively. The sewage pH also changed from alkaline to neutral. The observed results indicated that sewage sludge bio char can effectively treat sewage wastewater.
In this study, an assessment of the available sources of biomass and the associated technologies ... more In this study, an assessment of the available sources of biomass and the associated technologies are given for possible energy efficiency improvement. Bio char, a by product of biomass carbonization was assessed as a potential soil amendment as well as nutrient cycle agent. Bio energy is 80% efficient and if sustainable technologies are adopted the value can be increased so that the bio char available also increases. Usage of bio char in soil amendment improves the soil moisture content and has potential to act as a liming agent. High crop yields of up to 140% have been reported upon bio char use with application rates of at least 10 tons/hectare in field crops. The behaviour is attributed to the Terra preta effect caused by bio char and also increased micro organisms' habitants in the soil. However, several gaps such as the effect of carbonization temperature, source of biomass and its loading and their effects on nutrient cycling on the soil and plants still need to be understand in order to improve the nutrient cycling effects as well as the biomass cycle.
Tea wastes are generated on a daily basis in tea estates and these pose an environmental threat d... more Tea wastes are generated on a daily basis in tea estates and these pose an environmental threat due to greenhouse gases emissions yet these presents an opportunity of generation of biomass briquettes. In this study, tea wastes were converted to bio char at 300°C and ground to a particle size of less than 8mm. The bio char was compacted to form briquettes with a calorific value of 22-24 MJ/kg and moisture content of less than 10%. The tea waste briquettes can be integrated back into the tea manufacturing system as a co firing agent with coal or as an independent energy generator.
This study focused on the investigation of bio treatment of brewery wastewater using engineered m... more This study focused on the investigation of bio treatment of brewery wastewater using engineered micro organisms like Hycura. Brewery wastewater was treated in a 10L tank over a 5 day period with Hycura loadings of 0.05 g/L. The wastewater chemical oxygen demand (COD), biological oxygen demand (BOD), pH, total suspended solids (TSS), total Kjeldahl nitrogen (TKN) and total phosphates (TP) were measured using standard methods on a daily basis. The ph of the brewery waste changed from alkaline to neutral during the treatment process whilst the COD reduced by 87%, BOD by 88%, TSS by 94%, TKN by 68% and TP by 81%. The effective bio treatment of the brewery wastewater is attributed to the metabolism of Hycura.
The production of alternative energy sources from waste residues is increasingly becoming popular... more The production of alternative energy sources from waste residues is increasingly becoming popular. This paper focuses on the value addition of brewery spent grains waste by converting it to bio coal using hydrothermal carbonization. Brewery spent grains (BSG) from a local brewery company were used to determine the potential of making bio coal that can be used as a replacement to the conventional fossil fuel. Hydrothermal carbonization was conducted at 200 °C at a pressure of 25 bars for a residence time of 2 hours. The BSG were mixed with wastewater in the ratio 5:1. The bio coal that was produced had a calorific value of 26.1 MJ/kg and a fixed carbon content of 53.1%. The calorific values and fixed carbon were slightly higher than the conventional fossil coal which is an indication than BSG provides an alternative source of raw material for bio coal production, a source of renewable energy.
Due to waster scarcity, several cheap and user friendly technologies are being adopted to improve... more Due to waster scarcity, several cheap and user friendly technologies are being adopted to improve the efficiency in operation of wastewater treatment plants. In this study, Hycura, an engineered biocatalyst is proposed for use as a bio nutrient removal catalyst in municipal wastewater in a bid to enhance the treatment methods and improve the quality of effluent being disposed. The effectiveness of bio nutrient removal was measured through the biological oxygen demand (BOD), the chemical oxygen demand (COD), the total Kjeldahl nitrogen (TKN) and the total phosphates (TP) ratios. The COD/BOD ratios were >1.25, whilst the BOD/TKN ratios were >4.2, the COD/TKN ratios were >8.0 and the COD/TP ratios were >15. The ratios indicated a high bio degradability of bio nutrients from the municipal wastewater enhancing bio contaminants removal upon addition of Hycura to the system.
In this study, the potential to generate electricity from sewage sludge biogas harnessed from mun... more In this study, the potential to generate electricity from sewage sludge biogas harnessed from municipal sewage plants was investigated. Two sewage plants Crow borough and Marlborough were investigated as the potential raw material suppliers for the biogas generation. Sewage sludge samples were collected sand analyses for the total solids (TS), volatile solids (VS) and chemical oxygen demand (COD) among other parameters. Biogas generation was quantified in 250 mL flasks conducted under anaerobic conditions at mesophilic temperatures of 37 °C and thermophilic temperatures of 55 °C and agitation rates of 200 rpm. Optimum biogas production was achieved at 37 °C and 200 rpm with a methane composition of 72% before upgrading. The sewage sludge digestion to biogas was confirmed by the decrease in both TS and VS by 25.4% and 14.5% respectively. The average biogas generation rate was 0.015 m 3 /L with a Wobbe index of 24.78 indicating the high calorific value of the biogas and its potential to be generated to electricity.
In this study, the co-briquetting of coal fines saw dust and molasses as a binder is explored as ... more In this study, the co-briquetting of coal fines saw dust and molasses as a binder is explored as an option for value addition of the wastes generated in the various industries. The effect of the saw dust concentration and the molasses concentration was investigated through measuring the briquette's calorific value, fixed carbon, com-pressive strength and shatter index. Addition of Ca(OH) 2 was done to effect removal of sulphur from the bri-quette. Measurements of the briquettes physicochemical properties such as moisture content, ash content and sulphur content were measured using the standard methods. As the saw dust and the molasses concentration increased, the calorific value, fixed carbon and compressive strength increased by 16%, 8% and 50% respectively. Whereas, the shatter index decreased by 146% as the saw dust and the molasses concentration increased in relation to the coal fines. Addition of the saw dust and the molasses are therefore critical in the production of a high quality coal-saw dust-molasses briquette which does not shatter.
In this study, paper mill sludge was converted to biochar using the pyrolysis technology for appl... more In this study, paper mill sludge was converted to biochar using the pyrolysis technology for application in wastewater treatment. Paper mill sludge was pyrolyzed at 400-1000°C at a heating rate of 10°C/minute and carbonizing time of 45 minutes in a lab scale pyrolysis reactor. The biochar was ground to particle size of 1.8 mm and surface area of 500 m2/g and activated using steam. The paper mill biochar was loaded in a lab made adsorption column with a radius of 1.5 cm and length of 20 cm at a loading of 0.02 g/cm3 and used for treatment of textile wastewater as a bio-adsorbent. The change in the textile wastewater total dissolved solids (TDS), total suspended solids (TSS) and chemical oxygen demand (COD). The optimal adsorption time was 15 seconds, and this resulted in increased absorbance and transmittance in the treated effluent. Furthermore, the treated effluent TDS, TSS and COD significantly reduced by more than 97% upon using the paper mill biochar as an adsorbent. After consideration of a textile wastewater treatment plant treating 263 mega liters of wastewater per annum, a total capital investment of $ 67800 is required for the modified adsorption process with biochar costing $30/kg. The return on investment was found to be 52% with a payback period of 1.9 years. Profit will start to be realized after treating 140000 m3 of textile wastewater.
In this present study, Jatropha Carcus cake, a by product from the bio diesel production process ... more In this present study, Jatropha Carcus cake, a by product from the bio diesel production process was destabilization through vermicomposting to produce bio fertilizers. Jatropha Curcas cake was vermicomposted over a period 30 days using Eisenia Fetida earthworms. The nitrogen, phosphorous and potassium (NPK) content in the cake was continuously monitored using AOAC methods and the same was done for the leachate (vermiwash) produced during the vermicomposting process. The NPK content in the Jatropha Curcas cake increased with increase in the vermicomposting period with a 35% increase in N, 58% increase in P and a 98% increase in K. Furthermore, the vermiwash produced had an NPK with a composition of 2.1%, 0.75% and 0.51% respectively. The bio stabilization of the Jatropha Curcas cake through vermicomposting to bio fertilizers.
The brewery industry is one of the major industries in Zimbabwe and the following study was condu... more The brewery industry is one of the major industries in Zimbabwe and the following study was conducted to assess the techno-economic feasibility of reuse of wastewater after treatment using the biofilm that forms on the bio carriers. The malting plant of a certain brewing plant uses up to 350000 cubic meters water a year discharging about 75% of the biologically contaminated water as effluent which is discharged into the ecosystem. A biological water treatment approach was done using a moving bed biofilm reactor, with use of Mutag biochips. The treatment resulted in 93% BOD reduction, 87.9% COD reduction, 48% TSS reduction, 44% TDS reduction and a 97.8% increase in DO at a treatment period of 24 hours. An economic analysis was done with a payback period of 2.09 years and return on investment of 49% indicating the techno-economic viability of brewery wastewater.
This study investigated the potential to harvest biogas from tea waste as a resource recovery and... more This study investigated the potential to harvest biogas from tea waste as a resource recovery and waste management initiative. The tea waste was shredded to a particle size of less than 2.5 mm and anaerobically digested over a period of 30 days in 10-L digesters. The composition of biogas obtained was 60% to 65% methane with a yield of 0.2 L/g of tea waste feedstock. A reduction in the tea waste chemical oxygen demand and volatile solids composition by more than 50% indicated that optimal tea waste digestion had occurred. The tea waste digestate was rich in nitrogen (4.5%), phosphorous (0.6%), and potassium (4.6%) and could potentially be adopted as a biofertilizer. Biogas and biosolids can be generated from tea waste as a waste to resource initiative.
The potential to produce biogas and bio hydrogen from corn residue was investigated. A sample of ... more The potential to produce biogas and bio hydrogen from corn residue was investigated. A sample of 10g initially hydrothermally treated to liberate the cellulose and hemicellulose rich hydrolysate. Three steps for treatment at 80 • C for 15 min; 180 • C for 40 min and 190 • C and 10 min were investigated for corn residue conversion to soluble sugars. The highest cellulose yield was 0.356g per gram of corn residues through fermentation and 0.312g of bio hydrogen per gram of corn residues. An industrial process for the co-generation of biogas and bio-hydrogen from corn stover was then proposed from the experimental work.
Landfill organic waste fraction was investigated for the potential to generate bio ethanol, a liq... more Landfill organic waste fraction was investigated for the potential to generate bio ethanol, a liquid bio fuel that can be used in place of the conventional liquid fuels. This was achieved through acid treatment enzymatic hydrolysis. The organic fraction waste was first pre-treated with dilute sulphuric acid at 121 °C for 15 minutes. Afterwards it underwent enzymatic hydrolysis at 50 °C for a period of 5 days to allow the release of C6 sugars. The hydrolysate was then fermented at 30 °C for 5 days with yeast inoculated as the bio catalyst to produce bio ethanol. Enzymatic hydrolysis and the prior pre-treatment resulted in a high yield of 60% of the C6 sugars. The bio ethanol produced from the fermentable sugars was 40%. There is potential for utilization of the organic municipal waste fraction for bio fuels production.
This paper presents the treatment of municipality water using watermelon (Citrullus lanatus) seed... more This paper presents the treatment of municipality water using watermelon (Citrullus lanatus) seeds as natural coagulants and bio filter in the water treatment process. A significant reduction in water physicochemical parameters was observed notably the BOD and COD by more than 79% to meet the WHO guidelines for drinking water. A process treating 25 m 3 /day of the water for portable uses was processed and the design of the bio filter presented. An economic assessment for applying this technology in water treatment indicated a payback period of 10 months and a rate of return of 28% after investing $294 927.00.
Huge amounts of wastewater are being deposited in water bodies from industries, yet these can be ... more Huge amounts of wastewater are being deposited in water bodies from industries, yet these can be recycled to curb the water challenges while producing a renewable source of energy (biogas) as an initiative towards a green economy. In this study, dairy wastewater was used as a case study employing the membrane bioreactor and nanofiltration for wastewater treatment, while harnessing biogas in a fluidized bed biodigester bio augmented with Acti-zyme. There was 98.7% removal of TSS, 93.9% COD reduction, 95% BOD 5 reduction as well 90% color removal after membrane bioreactor treatment of the wastewater sample. A 99% removal of COD, 97% removal of BOD 5 , 99.9% removal for total solids, 99.9% removal of nutrients was also achieved with a 75% recovery of water. A 78% yield of biogas was realized from the biodigester at an optimum temperature of 37 o C. Integrated wastewater treatment supports water sustainability while creating clean, renewable and sustainable energy.
This paper focuses on an alternative biological method for piggery wastewater treatment using the... more This paper focuses on an alternative biological method for piggery wastewater treatment using the modified single stage vermifiltration process. A 3-stage vermifiltration process was used for piggery wastewater treatment as an alternative and modified biological wastewater treatment technique. Three vermifilters with media which comprised of Eisenia Fetida earthworms, garden soil, sand and quartz stones were used as the filtration media. The piggery wastewater chemical oxygen demand (COD), biological oxygen demand (BOD 5), total suspended solids (TSS), total dissolved solids (TDS), electrical conductivity (EC), manganese ions (Mn 2+) and dissolved oxygen (DO) values were measured before and after treatment with the vermifiltration at each stage. The parameters were measured using standard methods. Treatment using a 3-stage vermifilter connected in series resulted in 99.2% reduction in COD, 99.4% in BOD 5 , 99.2% in TSS, 80.2% in TDS, 86.9% in EC and 98% in Mn 2+. On the other hand, the DO concentration increased by >345.5%. Application of the 3-stage vermifiltration process in piggery wastewater treatment allows for effective biological contaminant removal making it safe for disposal in accordance to effluent disposal guidelines.
Sludge generated from the wastewater treatment plant of a pulp and paper factory was used as feed... more Sludge generated from the wastewater treatment plant of a pulp and paper factory was used as feedstock for the preparation of biochar using fast pyrolysis followed by chemical activation with NaOH to make activated biochar (ABC). A process utilising 300 kg/day of waste paper mill sludge (PMS) was designed with a plant utilisation of 80%. A pyrolysis temperature of 500 o C and residence time of 2 h was used in a limited oxygen pyrolysis reactor producing biochar at a yield of 40 %. The biochar was activated using NaOH and heated for an hour at 70 o C to enhance the sorption properties of the ABC. The resulting ABC had a BET surface area of 492.02 m 2 /g, had decolourising properties and a pH of 7, hence applicable in wastewater treatment. A capital investment of US$1 860 729.47 is required and the plant life is 20 years, with a net present value of US$ 1 832 445.94. The rate of return is 29.6 %, return on investment is 26.9% and a payback period of 3.7 years. The production of ABC from PMS is economically feasible, with a product selling price of $30.00/kg.
The world is facing formidable challenges in meeting rising demands of clean water as the availab... more The world is facing formidable challenges in meeting rising demands of clean water as the available supplies are depleting due to extended droughts, population growth, more stringent health based regulations and competing demands from a variety of users. At the same time, wastewater treatment plants are using energy from the national grid rather than generating their own energy. Piggery farms and paper mills make use of a lot of water and thus contribute towards water shortage. The piggery farms produce a significant amount of wastewater which water can be effectively treated via anaerobic routes to harness biogas. On the other hand, paper mills are generate excessive amounts of sludge during paper making process. Secondary treatment of wastewater can therefore be used to make sludge based activated biochar which can be used in wastewater treatment. This work assessed the feasibility of using a compound from activated carbon from paper mill sludge (PMS) and Acti-zyme (a digestion bio-catalyst) to treat piggery wastewater anaerobically and co-capturing the biogas produced for energy usage. A piggery wastewater treatment plant generating 6000 m 3 /day of wastewater was considered and the change in the wastewater physicochemical properties was determined using standard methods. The amount of biogas produced was determined using a water displacement method for retention periods of 30 days at 37 °C. The use of Acti-zyme and PMS biochar compound at 50 g/m 3 reduced the piggery wastewater contaminants properties such as total solids, colour, pH and BOD 5 by >70%. The treated effluent met the set standards for effluent water disposal. Biogas was produced at a rate of 2.3 m 3 /m 3 .day with a bio-methane composition of about 78%.
The paper presents a study that was conducted to assess the techno-economic feasibility of a sorg... more The paper presents a study that was conducted to assess the techno-economic feasibility of a sorghum brewers spent grain (BSG) fired boiler unit to generate 1 megawatt of electricity for a certain brewery company. The brewery company is currently generating 24 tons per day of sorghum brewers spent grain biomass waste which was used as a source of boiler fuel for this work. After a full proximate analysis the sorghum brewers spent grain had an average heating value of 12.6 MJ/kg whilst coal had 19.9 MJ/kg indicating that it is feasible to generate electricity using sorghum brewers spent grain as a source of fuel, and that sorghum brewers spent grains can be used as an alternative to coal. A process for conversion of the BSG to electricity was proposed for a biomass boiler unit consuming 1100 kg/hr BSG, operating at 86% efficiency, maximum pressure of 9 bar and steam output of 1689kg/hr was designed to supply a one megawatt turbine generator. Pressure, temperature and flow control mechanisms were assessed as a safety consideration. An economic analysis was done with a total investment cost of USD$ 3.4 million, a payback period of 3.7 years, and a return on investment of 27.4%. BSG provide an alternative source of electricity for the brewery industry.
Proper waste management in developing countries is increasingly becoming popular, especially the ... more Proper waste management in developing countries is increasingly becoming popular, especially the use of engineered sanitary landfills. In this study, the classification, design, and operation of sanitary landfills are stated and suggestions made. The landfills were classified in accordance to waste type and population size. Leachate control mechanisms were put in place in a bid to avoid surface and underground water pollution. Several liner materials such as clay and geotextile material are recommended to avoid leachate perforating into the ground. Waste management is encouraged to be done through the cell system which must be compacted and covered on a daily basis. Resource recovery of biogas for power generation is recommended to recovery value from the waste as well as to lower landfill operation costs. Post-closure monitoring of the landfill must be done and recreation centers can be developed on the landfill as a rehabilitation strategy. Land filling is essential for proper waste management and is also governed by local acts.
Treatment of municipal sewage sludge is a problem in Zimbabwe. However, if the appropriate waste ... more Treatment of municipal sewage sludge is a problem in Zimbabwe. However, if the appropriate waste to energy technologies are applied, sewage plants can generate their own electricity thus minimizing municipalities' reliance on the already strained national grid. An experimental study was therefore conducted on the Chitungwiza, Firle and Crowborough sewage plants, assessing the potential to harness biogas for electricity generation. These plants have sewage treatment capacities of 19.6 ML/day, 140 ML/day and 54 ML/day, respectively. Plant tours and inspections of the plants were conducted and an understanding of the plant designs as well as the current process flow was attained. Particular emphasis was placed on establishing the availability and state of infrastructure available for the production, handling and storage of biogas. All three plants have bio-digesters on site, however, the Chitungwiza digesters are open at the top thus releasing gas to the atmosphere. Firle and Crowborough plants are equipped with the basic infrastructure for biogas generation and storage; however, major refurbishments are required. Samples of sewage sludge were collected from the plants and placed under conditions that mimic a typical digester, the resultant biogas was analysed. The biogas was predominantly composed of methane (53-65%), CO 2 (22-27%), trace gases such as H 2 S, N 2 and H 2 accounted for the balance. Experimental results revealed that the use of 50 g/m 3 Acti-zyme as a bio-catalyst increases the quantity of methane produced to 72-78%. Based on the experimental results and the design capacities of the plants, the estimated power generation potential was 0.57-1.20 MW, 4.2-8.1 MW and 1.53-4.56 MW for the Chitungwiza, Firle and Crowborough, respectively. These capacities vary depending on whether it is the wet or dry season. An economic assessment indicated the viability of harnessing biogas from the three plants especially after incorporating Acti-zyme as the digestion catalyst to actively increase the electricity generated.
Water scarcity is a global problem hence the need for sustainable wastewater management. Sewage, ... more Water scarcity is a global problem hence the need for sustainable wastewater management. Sewage, a form of wastewater is being disposed-of to river bodies untreated. Additionally, disposal of sewage sludge, a by-product from the sewage treatment process, is resulting in landfilling problems. This study focused on the sustainable anaerobic treatment of sewage, co-harnessing biogas and bio-solids as value added products utilizing Acti-zyme, an enzyme bio-catalyst through bio-augmentation. Emphasis was given to the optimum sewage treatment conditions for removal of bio-nutrients, biogas and bio-solids generation, kinetic and statistical modelling of the bio-nutrient removal in sewage as well as the biogas and bio-solids production from sewage sludge. A techno-economic analysis was then done to check the viability of applying this technology on a large scale. The biochemical properties for Acti-zyme were characterized for potential use in anaerobic sewage treatment with the aim of producing biogas. Acti-zyme was then used for sewage treatment at a temperature of 37 °C, agitation rate of 60 rpm, Acti-zyme loadings of 0-0.070 g/L and retention times of 0-60 days. The total Kjeldahl nitrogen (TKN), biochemical oxygen demand (BOD_5), total suspended solids (TSS), total dissolved solids (TDS), electrical conductivity (EC), pH, chloride ions concentration (CI^-), total phosphorous (TP), sulphate ions concentration (SO_4^(2-)), dissolved oxygen (DO) and the chemical oxygen demand (COD) of sewage were measured using standard methods. The bio-nutrient removal ratios from the sewage were determined and statistical modelling was carried out for the bio-nutrient removal ratios: The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP. The sewage sludge was anaerobically digested using Acti-zyme in order to obtain biogas and bio-solids. Sewage sludge loading of 5-10 g/L.d and mesophilic and thermophilic temperatures of 37 °C and 55 °C were applied. The biogas quantity produced was measured using the water displacement method. Samples of the biogas were analysed for bio-methane (CH_4), carbon dioxide (CO_2) and traces gases composition using gas chromatography. The bio-solids obtained were tested for nitrogen, phosphorous and potassium (NPK) content using uv-vis spectrophotometry. Kinetic modelling was carried out in MATLAB R2013A to simulate bio-methane production from sewage sludge. Statistical models for anaerobic sewage sludge digestion for generation of biogas and bio-solids utilizing Acti-zyme, were then simulated from the experimental data. SPSS Statistics 19.0 was used as the statistical modelling package at a p-value of 0.05. Capital budgeting techniques were then used for techno-economic assessment of sewage treatment recovering biogas and bio-solids. Acti-zyme was found to be immotile and contained catalase, proteolytic enzymes and amylase. Acti-zyme did not promote H_2 S production, making it useful in sewage treatment producing biogas. Sewage treatment using Acti-zyme resulted in >60% decrease of the sewage contaminants through bio-augmentation. Optimum sewage treatment conditions were obtained at 0.050 g/L Acti-zyme loading and retention time of 40 days. The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP ratios obtained were > 1.2, 4.0, 8.0 and 15.0 respectively. The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP bio-nutrient removal models were developed. Optimum biogas production was obtained at a sewage sludge loading of 7.5 g/L.d and Acti-zyme loading of 0.050 g/L with a 78% bio-methane composition was achieved at mesophilic temperatures of 37 °C. Bio-solids with 8.17, 5.84 and 1.34 % of NPK respectively were produced. The bio-methane production was simulated to the linear, exponential, logistics kinetic, exponential rise to a maximum, first order exponential model and the modified Gompertz kinetic models. The logistics kinetic model accurately simulated the bio-methane production with a k-value of 0.073 day-1. Furthermore, linear, quadratic, compound and exponential statistical models were tested and validated for the biogas and the bio-solids generation. The quadratic statistical models were significant for simulating biogas and bio-solids production respectively. A sewage plant with a capacity of 19.6 600 ML/day was considered for techno-economic assessment, with an operating efficiency of 60% and a life span of 20 years. $5.125/day of Acti-zyme were required for production of 12 769.69 kg/day for biogas costing $1.50/kg and 672.08 kg/day of bio-solids costing $16.00/50kg. A net benefit of $5 656 363.92 per annum for using the Acti-zyme technology in sewage digestion was forecasted, whilst a net energy of 1 387.33 KWh was set to be produced. An investment of $22 199 501.40 was required for kick-starting the project. A positive net present value of $1 186 239.23 was realized with an internal rate of return of 17.6% and a payback period of 5.9 years. For breakeven to be realised, only 183 059.16 KWh must be produced. The techno-economic assessment indicated it is viable to treat sewage using Acti-zyme as bio-augmentation catalyst; co-harnessing biogas and bio-solids as valued added products to an extent of contributing 0.04% to the Zimbabwe gross domestic product. Keywords: Acti-zyme, bio-augmentation, biogas, bio-nutrients, bio-solids, sewage treatment, statistical modelling, techno-economic analysis
Photo: Ninara/Flickr Creative Commons (showing a drought stricken Zimbabwe) Zimbabwe, a country i... more Photo: Ninara/Flickr Creative Commons (showing a drought stricken Zimbabwe) Zimbabwe, a country in the Sub Sahara Africa is not being spared by the negative effects of climate change. Climate change is a sudden change in weather patterns due to global warming mainly caused by human activities and other external factors like solar radiation and volcanic eruptions [1]. Zimbabwe has reported a decline in precipitation in the past 60 years and also global warming temperatures of up to 0.8 °C [2]. The impacts of climate change in Zimbabwe has resulted in the violation of what the United Nations is trying to achieve in terms of the sustainable development goals (SDGs). The poverty rate, famine and deforestation rate has significantly increased due to the climate change effects. Currently in other parts of Zimbabwe, people are trading a cow for a 50 kg bag of maize due to the poor rainfalls which adversely lead to drought that have affected the country. Maize is the staple food in Zimbabwe Under normal circumstances the average price of a cow is US$250-400 whilst a 50 kg bag of maize cost about $US50. Due to the low rainfalls and the drought, famine rate has also increased in the country, since no farming activities are taking place, it leads to poor farming activities and low soil quality due to lack of manure. This leads to a high dependence on food aid. This climate change effect violates SDG 1 and SDG 2 which seeks to end poverty and hunger respectively. Simulation on maize production at all sites showed a considerable amount of variation under climate change conditions and will not give good yields, thus making maize production a less viable activity under climate change conditions. The simulated changes in crop yields are driven by two factors: CO 2 enrichment and changes in climate. In the low-lying areas of southern Zimbabwe, for example, it is probable that climate change will turn the region into a non-maize-producing area, as exemplified by reduced maize production in Masvingo. If climate change becomes a reality, this area, which represents 42% of the communal area, will become even more marginal for maize production and the farming seasons could be 25% shorter than now [3]. Since farming, is one of the major income in Zimbabwe, the presence of drought due to climate change has resulted in high rates of prostitution by women and girls succumbing them to HIV/AIDS and related diseases. This affects the women and girls' general wellbeing and good wealth violating the SGG 3. Furthermore drought due to climate change, it takes away the right to decent work and economic growth as per the requirements of SDG 8. This effectively results also in women disempowerment making them more prone to abuse. In addition to that, climate change has resulted in people consuming poor water quality in Zimbabwe. The moment there is a drought; people tend to obtain their water from dirt and unsafe sources of water resulting in diseases like cholera and diarrhoea. This is not in line with goal number 7 of the SDGs which seeks at provision and access of clean water and sanitation access to everyone. Estimating
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Papers by Prof. Mercy M . M . Manyuchi (Pr. Eng; CEng, FZweIE)
the bio augmentation technology at the same time harnessing biogas and bio solids as value
added products. Wastewater sample were collected in 5L containers and the sludge was
separated from the liquid. The liquid and sludge were bio augmented with Acti-zyme with
loadings of 5g/L, 10g/L and 15 g/L and were left to settle over a period of 30 days under
anaerobic conditions. The wastewater and treated effluent BOD, COD, TKN, TP, TSS, TDS
and pH were measured using standard methods. Whereas the amount of biogas generated was
measured using the water displacement and its composition quantified. The BOD, COD,
TKN, TP, TSS, TDS were significantly reduced by 93%, 77%, 87%, 89%, 90% and 90%
respectively. The BOD/COD ratio was 0.72 initially and reduced to 0.21 for all the Actizyme
loadings. Biogas with a methane composition of 65-70% was recovered.
the bio augmentation technology at the same time harnessing biogas and bio solids as value
added products. Wastewater sample were collected in 5L containers and the sludge was
separated from the liquid. The liquid and sludge were bio augmented with Acti-zyme with
loadings of 5g/L, 10g/L and 15 g/L and were left to settle over a period of 30 days under
anaerobic conditions. The wastewater and treated effluent BOD, COD, TKN, TP, TSS, TDS
and pH were measured using standard methods. Whereas the amount of biogas generated was
measured using the water displacement and its composition quantified. The BOD, COD,
TKN, TP, TSS, TDS were significantly reduced by 93%, 77%, 87%, 89%, 90% and 90%
respectively. The BOD/COD ratio was 0.72 initially and reduced to 0.21 for all the Actizyme
loadings. Biogas with a methane composition of 65-70% was recovered.
The biochemical properties for Acti-zyme were characterized for potential use in anaerobic sewage treatment with the aim of producing biogas. Acti-zyme was then used for sewage treatment at a temperature of 37 °C, agitation rate of 60 rpm, Acti-zyme loadings of 0-0.070 g/L and retention times of 0-60 days. The total Kjeldahl nitrogen (TKN), biochemical oxygen demand (BOD_5), total suspended solids (TSS), total dissolved solids (TDS), electrical conductivity (EC), pH, chloride ions concentration (CI^-), total phosphorous (TP), sulphate ions concentration (SO_4^(2-)), dissolved oxygen (DO) and the chemical oxygen demand (COD) of sewage were measured using standard methods. The bio-nutrient removal ratios from the sewage were determined and statistical modelling was carried out for the bio-nutrient removal ratios: The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP. The sewage sludge was anaerobically digested using Acti-zyme in order to obtain biogas and bio-solids. Sewage sludge loading of 5-10 g/L.d and mesophilic and thermophilic temperatures of 37 °C and 55 °C were applied. The biogas quantity produced was measured using the water displacement method. Samples of the biogas were analysed for bio-methane (CH_4), carbon dioxide (CO_2) and traces gases composition using gas chromatography. The bio-solids obtained were tested for nitrogen, phosphorous and potassium (NPK) content using uv-vis spectrophotometry. Kinetic modelling was carried out in MATLAB R2013A to simulate bio-methane production from sewage sludge. Statistical models for anaerobic sewage sludge digestion for generation of biogas and bio-solids utilizing Acti-zyme, were then simulated from the experimental data. SPSS Statistics 19.0 was used as the statistical modelling package at a p-value of 0.05. Capital budgeting techniques were then used for techno-economic assessment of sewage treatment recovering biogas and bio-solids.
Acti-zyme was found to be immotile and contained catalase, proteolytic enzymes and amylase. Acti-zyme did not promote H_2 S production, making it useful in sewage treatment producing biogas. Sewage treatment using Acti-zyme resulted in >60% decrease of the sewage contaminants through bio-augmentation. Optimum sewage treatment conditions were obtained at 0.050 g/L Acti-zyme loading and retention time of 40 days. The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP ratios obtained were > 1.2, 4.0, 8.0 and 15.0 respectively. The COD⁄〖BOD〗_5 , 〖BOD〗_5⁄TKN, COD/TKN and the COD/TP bio-nutrient removal models were developed. Optimum biogas production was obtained at a sewage sludge loading of 7.5 g/L.d and Acti-zyme loading of 0.050 g/L with a 78% bio-methane composition was achieved at mesophilic temperatures of 37 °C. Bio-solids with 8.17, 5.84 and 1.34 % of NPK respectively were produced. The bio-methane production was simulated to the linear, exponential, logistics kinetic, exponential rise to a maximum, first order exponential model and the modified Gompertz kinetic models. The logistics kinetic model accurately simulated the bio-methane production with a k-value of 0.073 day-1. Furthermore, linear, quadratic, compound and exponential statistical models were tested and validated for the biogas and the bio-solids generation. The quadratic statistical models were significant for simulating biogas and bio-solids production respectively.
A sewage plant with a capacity of 19.6 600 ML/day was considered for techno-economic assessment, with an operating efficiency of 60% and a life span of 20 years. $5.125/day of Acti-zyme were required for production of 12 769.69 kg/day for biogas costing $1.50/kg and 672.08 kg/day of bio-solids costing $16.00/50kg. A net benefit of $5 656 363.92 per annum for using the Acti-zyme technology in sewage digestion was forecasted, whilst a net energy of 1 387.33 KWh was set to be produced. An investment of $22 199 501.40 was required for kick-starting the project. A positive net present value of $1 186 239.23 was realized with an internal rate of return of 17.6% and a payback period of 5.9 years. For breakeven to be realised, only 183 059.16 KWh must be produced. The techno-economic assessment indicated it is viable to treat sewage using Acti-zyme as bio-augmentation catalyst; co-harnessing biogas and bio-solids as valued added products to an extent of contributing 0.04% to the Zimbabwe gross domestic product.
Keywords: Acti-zyme, bio-augmentation, biogas, bio-nutrients, bio-solids, sewage treatment, statistical modelling, techno-economic analysis