Pretreatment of Rice Straw by Hydrogen Peroxide for Enhanced Methane Yield

A pretreatment process for hydrogen peroxide （H2O2） was optimized to enhance the biodegradation performance of rice straw and increase biogas yield. A determination experiment was conducted under predicted optimal conditions. Optimization was implemented using response surface methodology. The effects of biodegradation and the interactive effects of pretreatment time （PT）, H2O2 concentration （HC）, and substrate to inoculum ratio （S/I） on methane yield were investigated. The lignin, cellulose, and hemicellulose of rice straw were significantly degraded with increasing HC. The optimal conditions for the use of pretreated rice straw in anaerobic digestion were a 6.18-d PT, 2.68% HC （w/w total solid）, and 1.08 S/I; these conditions result in a methane yield of 288 mL g-1 volatile solids （VS）. A determination coefficient of 95.2% was obtained, indicating that the model used to predict the anabolic digestion process has a favorable fit with the experimental parameters. The determination experiment resulted in a methane yield of 290 mL g-1 VS, 88.0% higher than that of untreated rice straw. Thus, H2O2 pretreatment of rice straw can be used to improve methane yields during biogas production.

Effect of Variation in Co-Digestion Ratios of Matooke, Cassava and Sweet Potato Peels on Hydraulic Retention Time, Methane Yield and Its Kinetics

This paper presents the results of batch anaerobic co-digestion of matooke, cassava, and sweet potato peels and vines. These agricultural wastes and others form the biggest portion of household wastes in developing countries. However, they have remained an unexploited resource amidst the ever increasing needs of clean energy and waste disposal challenges. Efforts to use them individually as biogas substrates have been associated with process acidification failure resulting from their fast hydrolysis. The aim of this work was to exploit agricultural wastes is co-digestion among themselves and assess their effect on methane yield and its kinetics, pH and hydraulic retention time (HRT). Sixteen ratios of Matooke peels (MP), cassava peels (CP) and sweet potato peels (SP) were assessed in duplicate. Methane yield and its kinetics, pH and HRT demonstrated dependence on the proportion of substrates in the mixture. Depending on the ratio mixture, HRT increased to 15 days compared to less than 5 days for single substrates, hydrolysis rate constant (k) reduced to a range of 0.1 - 0.3 d-1 compared to single substrates whose k-values were above 0.5 d-1, pH was maintained in the range of 6.38 - 6.43 and CH4 yield increased by 15% - 200%. Ratios 2:1:0, 2:0:1, 0:1:2, 1:1:1 and 1:1:4 were consistent all through in terms of model fitting, having a positive synergetic effect on HRT, hydrolysis rate constant, lag phase and methane yield. However, more research is needed in maintaining the pH near the neutral for process stability assurance if household wastes are to be used as standalone substrates for biogas production without being co-substrates with livestock manure.

Enhancement of methane yield from cotton stalks by mechanical pre-treatment

Cotton stalks(CS)are lignocellulosic agricultural by-products,a potential source for biogas production,but pretreatment must be considered since hydrolysis is the rate-limiting stage for lignocellulosic biomass substrates.This study investigates the feasibility of mechanical pretreatment of CS to enhance methane production.Batch anaerobic digestion of CS samples with particle sizes ranging from 0.5 to 65 mm was carried out in 1 L eudiometer batch digesters for 48 days at 37◦C.Results showed that methane yield was inversely proportional to particle size,and the quality of biogas was good(54.0-55.2%CH_(4)).Significant increases in methane yield were observed with 20.3%and 26%for samples with a particle size of 3 mm and 0.5 mm,respectively,compared to untreated CS.The coefficient of anaerobic energy turnover was relatively low(20.2-25.5%).Reduction of the CS particle size to 3 mm or less is recommended to achieve effective methane conversion and decrease the retention time in an anaerobic digester from 31 to about 25 days.However,to offset the high energy demand required for grinding,further research should be conducted in combining size reduction with chemical and physicochemical pretreatment.

Lower temperature hydrothermal pretreatment improves the anaerobic digestion performance of spent cow bedding

The anaerobic digestion(AD)performance of spent cow bedding was investigated with different hydrothermal pretreatment(HP)conditions.Spent cow bedding was pretreated with low temperatures(50,70,and 90℃)and different pretreatment times(2-72 h)with ammonia and without ammonia.The results showed that spent cow bedding was a good raw material for AD.After pretreatment,the concentration of volatile fatty acids(VFAs)in the group of hydrothermal pretreatments with ammonia(HPA)was higher than that in the HP group at the same pretreatment temperature and time.The optimal pretreatment condition was achieved with an HPA of 50℃ holding for 72 h.At the optimal condition,the highest concentration of VFAs was 1.58-10.85 times higher than that of the other pretreated groups.The highest hemicellulose and lignin removal rates were 58.07%and 10.32%,respectively.The highest methane yield was 163.0 ml(g· VS)^(-1),which was 48.9%higher than that of the untreated group.The VFAs,pH,and reducing sugars showed positive relationships with the methane yield.Therefore,HP at low temperature can enhance the AD performance of spent cow bedding.

ALKALINE PRETREATMENT AND AIR MIXING FOR IMPROVEMENT OF METHANE PRODUCTION FROM ANAEROBIC CO-DIGESTION OF POULTRY LITTER WITH WHEAT STRAW

Alkaline pretreatment(AL)and air mixing(air)both have the potential to improve anaerobic co-digestion(Co-AD)of poultry litter with wheat straw for methane production.In this study,the effects of the combination of AL(pH 12 for 12 h)and air mixing(12 mL·d^(−1))on the Co-AD process were investigated.The substrate hydrolysis was enhanced by AL,with soluble chemical oxygen demand increased by 4.59 times and volatile fatty acids increased by 5.04 times.The cumulative methane yield in the group of Co-AD by AL integrated with air(Co-(AL+air)),being 287 mL·(g VS_(added))^(−1),was improved by 46.7%compared to the control.The cone model was found the best in simulating the methane yield kinetics with R^(2)≥0.9979 and root mean square prediction error(rMSPE)≤3.50.Co-(AL+air)had a larger hydrolysis constant k(0.14 d^(−1))and a shorter lag phaseλ(0.99 d)than the control(k=0.12 d^(−1),λ=2.06 d).The digestate improved the removal of total solids and total volatile solids by 2.0 and 2.3 times,respectively.AL facilitated substrate degradation,while air can enrich the microbial activity,together enhancing the methane generation.The results show that AL+air can be applied as an effective method to improve methane production from the Co-AD process.

Anaerobic treatment of fresh leachate from a municipal solid waste incinerator by upflow blanket filter reactor

This paper describes the feasibility of fresh leachate treatment by an upflow blanket filter(UBF).Through dilution and partial effluent recycling,the organic loading rates increased from 0.51 to 14.56 kg COD/(m^(3)·d),meanwhile the corresponding hydraulic retention time decreased from 9.0 to 3.6 d.The reactor was able to achieve steady-state within 80 d.Based on the distribution of COD fluxes in the process,it was concluded that anabolism was the main pathway of COD removal in the initial phase(1–33 d),accounting for 57%–85%of total COD removed.As the anaerobic consortium of bacteria reached steady-state(after 70–86 d),the majority of COD removed was transformed into methane,because the specific methane yield was close to the theoretical value(0.36 L CH4/(g CODdeg)).

Fly ash and zero-valent iron-based in situ advanced anaerobic digestion with emphasis on the removal of antibiotics and antibiotic resistance genes from sewage sludge

This study investigated the removal of antibiotics and antibiotic resistance genes from sewage sludge by using fly ash(FA)-based in situ advanced anaerobic digestion(AAD)under mesophilic conditions.Five antibiotics(sulfadiazine,sulfameth-oxazole,ofloxacin,tetracycline,and roxithromycin)and 11 corresponding antibiotic resistance genes(Ib-cr,qnrS,ermF,ermT,ermX,sul1,sul2,sul3,tetA,tetB,and tetG)were selected as the targets.Adding FA to anaerobic digestion to remove antibiotics and resistance genes allows waste to be treated with waste.FA-based in situ AAD of sewage sludge effectively enhanced the process stability and methane yield,and the optimal FA-added dosage was 50 mg/L.The cumulative methane yield could be well described with the improved Gompertz model.FA addition effectively increased the overall removal of ofloxacin,by up to 85.3%at 50 mg/L FA and 10μg/L antibiotics,and the combination of zero-valent iron and FA enhanced only the overall removal of ofloxacin to 92.4%and tetracycline to 85.6%.However,FA-based in situ AAD could not enhance the overall removal of other antibiotics from sewage sludge.Not all the same types of antibiotic resistance genes were strongly positively correlated with the concentrations of antibiotics.The removal of antibiotic resistance genes influenced by FA addition varied largely with the types of antibiotic resistance genes,FA dosage,antibiotic content,and the combination with zero-valent iron.FA addition could not be verified to enhance the removal of antibiotic resistance genes.The addition of FA or zero-valent iron and the antibiotic concentrations significantly changed the microbial community structure during in situ AAD,and the combination of zero-valent iron and FA significantly reduces the species diversity and microbial abundance.The most abundant bacteria were Methanogarcina,Methanoberium,unidentified_Archaea,Terrimonas,Methomethoxychlo-rovorans,and Candidatus_Cloacimonas in the ZVI-FA test.