Effect of wastewater composition on the calcium carbonate precipitation in upflow anaerobic sludge blanket reactors

Calcium carbonate often precipitates in anaerobic reactors treating wastewater with high calcium content.The aim of this paper is to study the effect of wastewater composition on calcium carbonate precipitation in upflow anaerobic sludge blanket(UASB)reactors.Two laboratory-scale UASB reactors were operated with calcium-containing influents using acetate and carbohydrate as substrate,respectively.There was an obvious accumulation of inorganic precipitate observed in the biogranules.Observations via scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)showed that the acclimated biogranules in the two reactors differed in microstructure.Calcium carbonate was found to have precipitated on the surface of acetate-degrading biogranules,but precipitated at the core of the carbohydrate-degrading biogranules.The results indicated that substrates had significant influence on the location of calcium carbonate precipitation in anaerobic granular sludge,which was expected due to the different methanogens distribution and pH gradient within the granular sludge degrading various substrates.Moreover,the location of calcium carbonate precipitation substantially affected the specific methanogenic activity(SMA)of the granular sludge.The SMA of the acetate-degrading biogranules dropped from 1.96 gCODCH4·gVSS^(–1)·d^(–1)to 0.61 gCODCH4·gVSS^(–1)·d^(–1)after 180-d of operation in the reactor.However,the SMA of the carbohydrate-degrading biogranules was not adversely affected by calcium carbonate precipitation.

H_2S removal in landfill leachate treatment using UASB reactor

Leachate from a sanitary landfill site in Chengdu, China is treated using a hybrid-UASB reactor at pilot scale. H2S, resulting from the anaerobic bioconversion process of sulfate-reducing bacteria（SRB）, inhibits the growth and activity of methane-producing bacteria（MPB）and poses serious problems of pollution, so FeCl3is used for H2S removal. The results show that the system performs well in the treatment process. COD removal generally increases with the increase in the organic loading rate（OLR）, while the sulfate removal decreases slowly. As the OLR is higher than 7 kgCOD/（m3·d）, both COD and sulfate removal tend to be stable. When the reactor is operated at the design load of 9 kgCOD/（m3·d）, COD and sulfate removal remain about 79% and 91%, respectively. At the same time, the percentage of COD removed by SRB（CODSRB）also decreases from 8.9% to 4.0%. With FeCl3 addition, COD removal increases to 83%, while sulfate removal and CODSRBfurther decrease to 89% and 1.89%, respectively. According to the mass balance, nearly 82% of the sulfur is prevented from converting into H2S. Moreover, when the FeCl3 dosage is more than 1.6 g/L leachate, H2S can be removed totally from the biogas. Therefore, the application of FeCl3 for H2S removal in leachate treatment using the UASB reactor is very suitable and viable.

Acid resistance of methanogenic bacteria in a two-stage anaerobic process treating high concentration methanol wastewater

In this study,the two-stage upflow anaerobic sludge blanket(UASB)system and batch experiments were employed to evaluate the performance of anaerobic digestion for the treatment of high concentration methanol wastewater.The acid resistance of granular sludge and methanogenic bacteria and their metabolizing activity were investigated.The results show that the pH of the first UASB changed from 4.9 to 5.8 and 5.5 to 6.2 for the second reactor.Apparently,these were not the advisable pH levels that common metha-nogenic bacteria could accept.The methanogenic bacteria of the system,viz.Methanosarcina barkeri,had some acid resis-tance and could still degrade methanol at pH 5.0.If the meth-anogenic bacteria were trained further,their acid resistance would be improved somewhat.Granular sludge of the system could protect the methanogenic bacteria within its body against the impact of the acidic environment and make them degrade methanol at pH 4.5.The performance of granular sludge was attributed to its structure,bacteria species,and the distribution of bacterium inside the granule.

Microbial community dynamics at high organic loading rates revealed by pyrosequencing during sugar refinery wastewater treatment in a UASB reactor

The performance and rnicrobial community structure in an upflow anaerobic sludge blanket reactor （UASB） treating sugar refinery wastewater were investigated. The chemical oxygen demand （COD） removal reached above 92.0% at organic loading rates （OLRs） of 12.0-54.0 kgCOD/（m^3· d）. The volatile lhtty acids （VFAs） in effluent were increased to 451.1 mg/L from 147.9 mg/L and the specific methane production rate improved by 1.2 2.2-1bid as the OLR increased. The evolution of microbial comnmnities in anaerobic sludge at three different OLRs was investigated using pyrosequencing. Operational taxonomic units （OTUs） at a 3% distance were 353,337 and 233 for OLRI2, OLR36 and OLR54, respectively. When the OLR was increased to 54.0 kgCOD/（m^3· d） from 12.0 kgCOD/ （m^3· d） by stepwise, the microbial community structure were changed significantly. Five genera （Bacteroides, Trichococcus, Cho,seobacterium, Longilinea and Aerococcus） were the dominant fermentative bacteria at the OLR 12-0 kgCOD/（m^3· d）. However, the sample of OLR36 was dominated by Lacmcoccus, Trichococcus, Anaer-arcus and Veillonella. At the last stage （OLR = 54.0 kgCOD/ （m^3· d）, the diversity and percentage of femlentative bacteria were markedly increased. Apart from fermentative bacteria, an obvious shift was observed in hydrogen-producing acetogens and non- acetotrophic methanogens as OLR increased. Svntrophohacter, Geobacter and Methanomethylovor- ans were the dominant hydrogen-producing acetogens and methylotrophic methanogens in the samples of OLRI2 and OLR36. When the OLR was increased to 54.0 kgCOD/（m^3· d）, the mare hydrogen-producing acetogens and hydrogenotrophic methanogens were substituted with Destd/bvi- brio and Methanospillum. However, the composition of acetotrophic methanogens （Methanosaeta） was relatively stable during the whole operation period of the UASB reactor.