An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter（AF） was introduced for the treatment of coal gasification wastewater（CGW）,and effluent recirculation was adopted to enhance phenol removal and methane production.The results indicated that AF was reliable in treating diluted CGW,while its efficiency and stability were seriously reduced when directly treating raw CGW.However,its performance could be greatly enhanced by effluent recirculation.Under optimal effluent recirculation of 0.5 to the influent,concentrations of chemical oxygen demand（COD） and total phenol in the effluent could reach as low as 234.0 and 14.2 mg/L,respectively.Also,the rate of methane production reached 169.0 m L CH_4/L/day.Though CGW seemed to restrain the growth of anaerobic microorganisms,especially methanogens,the inhibition was temporary and reversible,and anaerobic bacteria presented strong tolerance.The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater（GW）.However,the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication.By analysis using the Haldane model,it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters,but only suitable effluent recirculation could result in high methanogenic activity.

Effect of the chlortetracycline addition method on methane production from the anaerobic digestion of swine wastewater

Effects of antibiotic residues on methane production in anaerobic digestion are commonly studied using the following two antibiotic addition methods：（1） adding manure from animals that consume a diet containing antibiotics, and（2） adding antibiotic-free animal manure spiked with antibiotics. This study used chlortetracycline（CTC） as a model antibiotic to examine the effects of the antibiotic addition method on methane production in anaerobic digestion under two different swine wastewater concentrations（0.55 and 0.22 mg CTC/g dry manure）. The results showed that CTC degradation rate in which manure was directly added at 0.55 mg CTC/g（HSPIKE treatment） was lower than the control values and the rest of the treatment groups. Methane production from the HSPIKEtreatment was reduced（p 〈 0.05） by 12% during the whole experimental period and 15% during the first 7 days. The treatments had no significant effect on the pH and chemical oxygen demand value of the digesters, and the total nitrogen of the0.55 mg CTC/kg manure collected from mediated swine was significantly higher than the other values. Therefore, different methane production under different antibiotic addition methods might be explained by the microbial activity and the concentrations of antibiotic intermediate products and metabolites. Because the primary entry route of veterinary antibiotics into an anaerobic digester is by contaminated animal manure, the most appropriate method for studying antibiotic residue effects on methane production may be using manure from animals that are given a particular antibiotic, rather than adding the antibiotic directly to the anaerobic digester.

A syntrophic propionate-oxidizing microflora and its bioaugmentation on anaerobic wastewater treatment for enhancing methane production and COD removal

Methane fermentation process can be restricted and even destroyed by the accumulation of propionate because it is the most difficult to be anaerobically oxidized among the volatile fatty acids produced by acetogenesis. To enhance anaerobic wastewater treatment process for methane production and COD removal, a syntrophic propionate-oxidizing microflora B83 was obtained from an anaerobic activated sludge by enrichment with propionate. The inoculation of microflora B83, with a 1：9 ratio of bacteria number to that of the activated sludge, could enhance the methane production from glucose by 2.5 times. With the same inoculation dosage of the microflora B83, COD removal in organic wastewater treatment process was improved from 75.6% to 86.6%, while the specific methane production by COD removal was increased by 2.7 times. Hydrogen-producing acetogene_sis.appeared to be a rate-limiting step in methane termentation, and the enhancement orhydrogen-producing acetogens in the anaerobic wastewater treatment process had improved not only the hydrogen-producing acetogenesis but also the acidogenesis and methanogenesis.

Impact of food to microorganism ratio and alcohol ethoxylate dosage on methane production in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor

The effects of food to microorganism （FIM） ratio and alcohol ethoxylate （AE） dosage on the methane production potential were investigated in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor （SAnMBR）. The fate of AE and its acute and/or chronic impact on the anaerobic microbes were also analyzed. The results indicated that AE had an inhibitory effect to methane production potential （lag-time depends on the AE dosage） and the negative effect attenuated subsequently and methane production could recover at FIM ratio of 0.088-0.357. VFA measurement proved that AE was degraded into small molecular organic acids and then converted into methane at lower FIM ratio （FIM 〈 0.158）. After long-term acclimation, anaerobic microbe could cope with the stress of AE by producing more EPS （extracellular polymeric substances） and SMP （soluble microbial products） due to its self-protection behavior and then enhance its tolerance ability. However, the methane production potential was considerably decreased when AE was present in wastewater at a higher FIM ratio of 1.054. Higher AE amount and FIM ratio may destroy the cell structure of microbe, which lead to the decrease of methane production activity of sludge and methane production potential.

Optimization of microwave pretreatment of lignocellulosic waste for enhancing methane production： Hyacinth as an example

The effect of microwave pretreatment on the anaerobic degradation of hyacinth was investigated using response surface methodology （RSM）. The components oflignin and the other constituents of hyacinth were altered by microwave pretreatment. Comparison of the near-infrared spectra of hyacinth pretreated by microwave irradiation and water-heating pretreatment revealed that no new compounds were generated during hyacinth pretreatment by microwave irradiation. Atomic force microscopy observations indicated that the physical structures of hyacinth were disrupted by microwave pretreatment. The yield of methane per gram of the microwave-irradiated substrate increased by 38.3% as compared to that of the substrate pretreated via water-heating. A maximum methane yield of 221 mL·g-sub^-1 was obtained under the optimum pretreatment conditions （substrate concentration （pSC） = 20.1 g·L^-1 and pretreatment time （PT） = 14.6 min） using RSM analysis. A maximum methane production rate of 0.76 mL·h^-1· g-sub^-1 was obtained by applying PSC = 9.5 g·L^-1 and PT= 11 min. Interactive item coefficient analysis showed that methane production was dependent on the PSC and PT, separately, whereas the interactive effect of the PSC and PT on methane production was not significant. The same trend was also observed for the methane production rate.

A comparative study on the alternating mesophilic and thermophilic two-stage anaerobic digestion of food waste

An alternating mesophilic and thermophilic two stage anaerobic digestion （AD） process was conducted. The temperature of the acidogenic （A） and methanogenic （M） reactors was controlled as follows： System 1 （S1） mesophilic A-mesophilic M; （S2） mesophilic A-thermophilic M; and （S3） thermophilic A-mesophilic M. Initially, the AD reactor was acclimatized and inoculated with digester sludge. Food waste was added with the soluble chemical oxygen demand （SCOD） concentrations of 41.4-47.0 g/L and volatile fatty acids of 2.0-3.2 g/L. Based on the results, the highest total chemical oxygen demand removal （86.6%） was recorded in S2 while S3 exhibited the highest SCOD removal （96.6%）. Comparing S1 with S2, total solids removal increased by 0.5%;S3 on the other hand decreased by 0.1% as compared to S1. However, volatile solids （VS） removal in S1, S2, and S3 was 78.5%, 81.7%, and 79.2%, respectively. S2 also exhibited the highest CH4 content, yield, and production rate of 70.7%, 0.44 L CH4/g VSadded, and 1.23 L CH4/（L.day）, respectively. Bacterial community structure revealed that the richness, diversity, evenness, and dominance of S2 were high except for the archaeal community. The terminal restriction fragments dendrogram also revealed that the microbial community of the acidogenic and methanogenic reactors in S2 was distinct. Therefore, S2 was the best among the systems for the operation of two-stage AD of food waste in terms of CH4 production, nutrient removal, and microbial community structure.