Treatment of petrochemical secondary effluent by an up-flow biological aerated filter (BAF).

In this study, petrochemical secondary effluent was treated by a 55 cm diameter pilot-scale biological aerated filter (BAF) with a media depth of 220 cm. Volcanic rock grains were filled as the BAF media. Median removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) was 29.35 and 57.98%, respectively. Moreover, the removal profile of the COD, NH3-N, total nitrogen and total organic carbon demonstrated that the filter height of 140 cm made up to 90% of the total removal efficiency of the final effluent. By gas chromatography-mass spectrometry, removal efficiencies of 2-chloromethyl-1,3-dioxolane, and benzonitrile, indene and naphthalene were obtained, ranging from 30.12 to 63.01%. The biomass and microbial activity of the microorganisms on the filter media were in general reduced with increasing filter height, which is consistent with the removal profile of the contaminants. The detected genera Defluviicoccus, Betaproteobacteria_unclassified and the Blastocatella constituted 1.86-6.75% of the identified gene, enhancing the COD and nitrogen removal in BAF for treating petrochemical secondary effluent.

Enhanced anaerobic digestion of waste activated sludge of low organic content in a novel digester.

A novel digester, termed an internal circulation anaerobic digester (ICAD), was developed to intensify sludge digestion. It consists of reaction zone, settling zone, thickening zone, riser and downcomer. Internal circulation in the digester is intensified by backflow biogas. The mesophilic ICAD treating thermal pretreated waste activated sludge with volatile suspended solids (VSS)/suspended solids (SS) of 0.45-0.49 was conducted in this study to reduce and stabilize the low organic content sludge. The results showed that the VSS removal rate and biogas rate reached 46.0% and 0.72 m(3)/kg VSS(fed) at hydraulic retention time (HRT) of 15 days. VSS/SS and soluble chemical oxygen demand (SCOD) of the effluent sludge ranged from 0.39 to 0.41 and 274 mg/L to 473 mg/L, respectively, under various HRTs from 10 to 27 days. The degradation ability of ICAD derived from the improved mass transfer by internal circulation and long solid retention time at short HRT is compared with continuous stirred tank reactor.

Microbial activity and community structure in a lake sediment used for psychrophilic anaerobic wastewater treatment.

AIMS: The aim of the study was to investigate the feasibility of a continuous reactor for psychrophilic anaerobic wastewater treatment by using the sludge from cold natural environment. METHODS AND RESULTS: Six sludge samples (S1-S6) were collected from different cold natural locations to select sludge with high anaerobic microbial activity under low temperatures. After a 225-day incubation, the maximum specific methane production rate of a waterfowl lake sediment (S1) at 15°C (70·5mLCH(4) gVSS(-1) day(-1)) was much higher than all other samples. S1 was thus chosen as the seed sludge for the reactor treating synthetic brewery wastewater at 15°C, by immobilizing the micro-organisms on polyurethane foam carriers. The chemical oxygen demand (COD) removal efficiency reached over 80% after 240-day operation at an organic loading rate of 5·3kg m(-3) day(-1), and significant enrichment of biomass was observed. Clone libraries of the microbial communities in the inoculum had high diversities for both archaea and bacteria. Along with a decrease in microbial community diversities, the dominant bacteria (79·5%) at the end of the operation represented the phylum Firmicutes, while the dominant archaeon (41·5%) showed a similarity of 98% with the psychrotolerant methanogen Methanosarcina lacustris. CONCLUSIONS: The possibility of using anaerobic micro-organisms from cold environments in anaerobic wastewater treatment under psychrophilic conditions is supported by these findings. SIGNIFICANCE AND IMPACT OF THE STUDY: This study enriches the theory on microbial community and the application on anaerobic treatment of sludge from cold natural environments.

Reactor performance and microbial community of an EGSB reactor operated at 20 and 15 degrees C.

AIMS: To investigate the effects of low temperatures on the performance and microbial community of anaerobic wastewater treatment. METHODS AND RESULTS: An expanded granular sludge bed (EGSB) reactor was employed to treat synthetic brewery wastewater at 20 and 15 degrees C. Reactor performance was represented by chemical oxygen demand (COD) removal efficiency, while the microbial community was analysed using denaturing gradient gel electrophoresis (DGGE) and clone technology. When the hydraulic retention time (HRT) was maintained at 18 h, COD removal efficiencies above 85% were obtained at both 20 and 15 degrees C, with influent COD concentrations up to 7300 and 4100 mg l(-1), respectively. At 15 degrees C, the COD removal efficiency was more easily manipulated by increasing the influent COD concentration. DGGE and clone results for both temperatures revealed that Methanosaeta and Methanobacterium were two dominant methanogens, and that the majority of the eubacterial clones were represented by Firmicutes. When the temperature decreased from 20 to 15 degrees C, both archaeal and eubacterial communities had higher diversity, and the proportion of Methanosaeta (acetate-utilizing methanogens) decreased markedly from 60.0% to 49.3%, together with an increase in proportions of hydrogen-utilizing methanogens (especially Methanospirillum). CONCLUSIONS: The feasibility of psychrophilic anaerobic treatment of low and medium strength organic wastewaters was demonstrated, although lower temperature could significantly affect both reactor performance and the anaerobic microbial community. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings enrich the theory involving the microbial community and the application of anaerobic treatment in a psychrophilic environment.

Microbial community in granules from a high-rate EGSB reactor.

The spatial distribution, quantity and diversity of different microorganisms within anaerobic granular sludge from a lab-scale expanded granular sludge bed (EGSB) reactor operated at different organic loading rates were studied using florescent in situ hybridization (FISH), real time quantitative-polymerase chain reaction (RTQ-PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The results indicated that most Eubacteria were located in the outer layer of granule, while the Archaea which mainly were methanogens and more sensible to the environmental conditions were located in the inner layer of the granule. The quantity of Archaea was obviously less than that of Eubacteria in the granules, but increased with the increasing of organic loading rates of the reactor. As the organic loading rate of the reactor increased and the operating time elapsed, the Archaea community in the granules changed significantly. Seven typical DGGE bands were collected and sequenced, and found that the dominant species of Archaea in the granules operated in the last period were mainly Methanocorpusculum, Methanobacterium, Methanosaeta.

Flow pattern analysis of a full-scale expanded granular sludge bed-type reactor under different organic loading rates.

The hydraulic characteristics of a lab-scale and a full-scale (275 m(3)) expanded granular sludge bed (EGSB)-type reactor under different organic loading rates varying from 10 kg COD m(-3)d(-1) to 45 kg COD m(-3)d(-1) were investigated. A modified combined model composed of two completely mixing regions and a plug flow region was sufficient for simulating the flow pattern of a full-scale EGSB-type reactor. Moreover, the outputs fitted the measured tracer distribution results well. The simplified model structure was in very good agreement with the physical structure of a full-scale EGSB-type reactor. The upflow (liquid+gas) velocity, high concentration of granular sludge, and gas hold-up effect may contribute to the generation of dead spaces (maximum of 19.5%). The bed expansion characteristics indicated that the sludge bed of the EGSB-type reactor performed as a suspended bed, in which the bed expansion was controlled between 20% and 30%, rather than the usually considered expanded bed.