Wei Qiao

Biogas productivity by co-digesting Taihu blue algae with corn straw as an external carbon source

A batch anaerobic test was conducted to evaluate the effects of adding high carbon content of corn straw to the digestion of Taihu blue algae to attain an optimal C/N ratio for higher methane yield. The addition of corn straw in algae at a C/N ratio of 20/1 increased methane yield by 61.69% at 325 mL g(-1)VS(-1) (compared with 201 mL g(-1) VS(-1) of algae digestion alone), followed by C/N ratios of 16/1 and 25/1, all operated at 20 g VSL(-1) and 35 °C. The results suggest the optimal C/N ratio for co-digestion of algae with corn straw is 20/1. The findings could offer options for efficient methane production and waste treatment.

Effect of biological pretreatments in enhancing corn straw biogas production

A biological pretreatment with new complex microbial agents was used to pretreat corn straw at ambient temperature (about 20°C) to improve its biodegradability and anaerobic biogas production. A complex microbial agent dose of 0.01% (w/w) and pretreatment time of 15 days were appropriate for biological pretreatment. These treatment conditions resulted in 33.07% more total biogas yield, 75.57% more methane yield, and 34.6% shorter technical digestion time compared with the untreated sample. Analyses of chemical compositions showed 5.81-25.10% reductions in total lignin, cellulose, and hemicellulose contents, and 27.19-80.71% increases in hot-water extractives; these changes contributed to the enhancement of biogas production. Biological pretreatment could be an effective method for improving biodegradability and enhancing the highly efficient biological conversion of corn straw into bioenergy.

Mesophilic methane fermentation of chicken manure at a wide range of ammonia concentration: stability, inhibition and recovery.

A 12L mesophilic CSTR of chicken manure fermentation was operated for 400 days to evaluate process stability, inhibition occurrence and the recovery behavior suffering TAN concentrations from 2000 mg/L to 16,000 mg/L. A biogas production of 0.35-0.4 L/gVS(in) and a COD conversion of 68% were achieved when TAN concentration was lower than 5000 mg/L. Ammonia inhibition occurred due to the addition of NH4HCO3 to the substrate. The biogas and COD conversion decreased to 0.3 L/gVS(in) and 20% at TAN 10,000 mg/L and was totally suppressed at TAN 16,000 mg/L. Carbohydrate and protein conversion decreased by 33% and 77% after inhibition. After extreme inhibition, the reactor was diluted and washed, reducing TAN and FA to 4000 mg/L and 300 mg/L respectively, and the recovered biogas production was 0.5 L/gVS(in). The extended Monod model manifested the different sensitivities of hydrolysis, acidogenesis and methanogenesis to inhibition. VFA accumulation accompanied an increase in ammonia and exerted a toxic on microorganism.

Remediation of petroleum-contaminated soil after composting by sequential treatment with Fenton-like oxidation and biodegradation

A laboratory study was conducted to enhance removal of residual contaminants after composting in a highly petroleum-contaminated soil by combining Fenton-like pretreatment with biodegradation. The contaminants were characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) during soil treatment. The optimum molar ratio of H(2)O(2) and Fe(3+) was 300/1 determined in batch experiments. At the end of Fenton-like treatment, total dichloromethane-extractable organics (TEO) decreased from 32,400 to 21,800 mg kg(-1) soil, and the toxicity of soil was reduced greatly in the preoxidation process. A significant loss of the number of soil microorganisms was observed in the Fenton-like reaction. During the microbial treatment period, 50.6% of TEO was destroyed. Numerous varieties of polar compounds containing nitrogen and oxygen were identified by FT-ICR MS. The number of compounds containing two oxygen atoms dropped from 604 to 163 during Fenton-like oxidation, and increased again to 577 after biodegradation.

Microbial community shifts and biogas conversion computation during steady, inhibited and recovered stages of thermophilic methane fermentation on chicken manure with a wide variation of ammonia

The thermophilic methane fermentation of chicken manure (10% TS) was investigated within a wide range of ammonia. Microbiological analysis showed significant shifts in Archaeal and Bacterial proportions with VFA accmulation and CH4 formation before and after inhibition. VFA accumulated sharply with lower methane production, 0.29 L/g VS, than during the steady stage, 0.32 L/g VS. Biogas production almost ceased with the synergy inhibition of TAN (8000 mg/L) and VFA (25,000 mg/L). Hydrogenotrophic Methanothermobacter thermautotrophicus str. was the dominate archaea with 95% in the inhibition stage and 100% after 40 days recovery compared to 9.3% in the steady stage. Aceticlastic Methanosarcina was not encountered with coincided phenomenal of high VFA in the inhibition stage as well as recovery stage. Evaluation of the microbial diversity and functional bacteria indicated the dominate phylum of Firmicutes were 94.74% and 84.4% with and without inhibition. The microbial community shifted significantly with elevated ammonia concentration affecting the performance.

Removal of residual contaminants in petroleum-contaminated soil by Fenton-like oxidation

The degradation of bioremediation residues by hydrogen peroxide in petroleum-contaminated soil was investigated at circumneutral pH using a Fenton-like reagent (ferric ion chelated with EDTA). Batch tests were done on 20 g soil suspended in 60 mL aqueous solution containing hydrogen peroxide and Fe(3+)-EDTA complex under constant stirring. A slurry reactor was used to treat the soil based on the optimal reactant conditions. Contaminants were characterized by Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the optimal treatment condition was: the molar ratio of hydrogen peroxide to iron=200:1, and pH 7.0. Under the optimum condition, total dichloromethane-extractable organics were reduced from 14,800 to 2300 mg kg(-1) soil when the accumulative H(2)O(2) dosage was 2.45 mol kg(-1) soil during the reactor treatment. Abundance of viable cells was lower in incubated Fenton-like treated soil than in untreated soil. Oxidation of contaminants produced remarkable compositional and structural modifications. A fused ring compound, identified as C(34)H(38)N(1), was found to exhibit the greatest resistance to oxidation.

Thermophilic anaerobic digestion of coffee grounds with and without waste activated sludge as co-substrate using a submerged AnMBR: System amendments and membrane performance

Coffee grounds are deemed to be difficult for degradation by thermophilic anaerobic process. In this research, a 7 L AnMBR accepting coffee grounds was operated for 82 days and failed with pH dropping to 6.6. The deficiency of micronutrients in the reactor was identified. The system was recovered by supplying micronutrient, pH adjustment and influent ceasing for 22 days. In the subsequent 160 days of co-digestion experiment, waste activated sludge (15% in the mixture) was mixed into coffee grounds. The COD conversion efficiency of 67.4% was achieved under OLR of 11.1 kg-COD/m(3) d and HRT of 20 days. Tannins was identified affecting protein degradation by a batch experiment. Quantitative supplements of NH4HCO3 (0.12 g-N/g-TSin) were effective to maintain alkalinity and pH. The solid concentration in the AnMBR reached 75 g/L, but it did not significantly affect membrane filtration under a flux of 5.1 L/m(2) h. Soluble carbohydrate, lipid and protein were partially retained by the membrane.

Effects of lipid concentration on anaerobic co-digestion of municipal biomass wastes.

The influence of the lipid concentration on the anaerobic co-digestion of municipal biomass waste and waste-activated sludge was assessed by biochemical methane potential (BMP) tests and by bench-scale tests in a mesophilic semi-continuous stirred tank reactor. The effect of increasing the volatile solid (VS) concentration of lipid from 0% to 75% was investigated. BMP tests showed that lipids in municipal biomass waste could enhance the methane production. The results of bench-scale tests showed that a lipids concentration of 65% of total VS was the inhibition concentration. Methane yields increased with increasing lipid concentration when lipid concentrations were below 60%, but when lipid concentration was set as 65% or higher, methane yields decreased sharply. When lipid concentrations were below 60%, the pH values were in the optimum range for the growth of methanogenic bacteria and the ratios of volatile fatty acid (VFA)/alkalinity were in the range of 0.2-0.6. When lipid concentrations exceeded 65%, the pH values were below 5.2, the reactor was acidized and the values of VFA/alkalinity rose to 2.0. The amount of Brevibacterium decreased with increasing lipid content. Long chain fatty acids stacked on the methanogenic bacteria and blocked the mass transfer process, thereby inhibiting anaerobic digestion.

Long-term stability of thermophilic co-digestion submerged anaerobic membrane reactor encountering high organic loading rate, persistent propionate and detectable hydrogen in biogas.

The performance of thermophilic anaerobic co-digestion of coffee grounds and sludge using membrane reactor was investigated for 148 days, out of a total research duration of 263 days. The OLR was increased from 2.2 to 33.7 kg-COD/m(3)d and HRT was shortened from 70 to 7 days. A significant irreversible drop in pH confirmed the overload of reactor. Under a moderately high OLR of 23.6 kg-COD/m(3)d, and with HRT and influent total solids of 10 days and 150 g/L, respectively, the COD removal efficiency was 44.5%. Hydrogen in biogas was around 100-200 ppm, which resulted in the persistent propionate of 1.0-3.2g/L. The VFA consumed approximately 60% of the total alkalinity. NH4HCO3 was supplemented to maintain alkalinity. The stability of system relied on pH management under steady state. The 16SrDNA results showed that hydrogen-utilizing methanogens dominates the archaeal community. The propionate-oxidizing bacteria in bacterial community was insufficient.

Biogas production from supernatant of hydrothermally treated municipal sludge by upflow anaerobic sludge blanket reactor.

The supernatant of hydrothermally treated sludge was treated by an upflow anaerobic sludge blanket (UASB) reactor for a 550-days running test. The hydrothermal parameter was 170°C for 60 min. An mesophilic 8.6L UASB reactor was seeded with floc sludge. The final organic loading rate (OLR) could reach 18 kg COD/m(3)d. At the initial stage running for 189 days, the feed supernatant was diluted, and the OLR reached 11 kg COD/m(3)d. After 218 days, the reactor achieved a high OLR, and the supernatant was pumped into the reactor without dilution. The influent COD fluctuated from 20,000 to 30,000 mg/L and the COD removal rate remained at approximately 70%. After 150 days, granular sludge was observed. The energy balance calculation show that heating 1.0 kg sludge needs 0.34 MJ of energy, whereas biogas energy from the supernatant of the heated sludge is 0.43MJ.