Anaerobic Processes as the Core Technology for Sustainable Domestic Wastewater Treatment: Consolidated Applications, New Trends, Perspectives, and Challenges

Anaerobic digesters have been responsible for the removal of large fraction of organic matter (mineralization of waste sludge) in conventional aerobic sewage treatment plants since the early years of domestic sewage treatment (DST). Attention on the anaerobic technology for improving the sustainability of sewage treatment has been paid mainly after the energy crisis in the 1970s. The successful use of anaerobic reactors (especially up-flow anaerobic sludge blanket (UASB) reactors) for the treatment of raw domestic sewage in tropical and sub-tropical regions (where ambient temperatures are not restrictive for anaerobic digestion) opened the opportunity to substitute the aerobic processes for the anaerobic technology in removal of the influent organic matter. Despite the success, effluents from anaerobic reactors treating domestic sewage require post-treatment in order to achieve the emission standards prevailing in most countries. Initially, the composition of this effluent rich in reduced compounds has required the adoption of post-treatment (mainly aerobic) systems able to remove the undesirable constituents. Currently, however, a wealth of information obtained on biological and physical-chemical processes related to the recovery or removal of nitrogen, phosphorus and sulfur compounds creates the opportunity for new treatment systems. The design of DST plant with the anaerobic reactor as core unit coupled to the pre- and post-treatment systems in order to promote the recovery of resources and the polishing of effluent quality can improve the sustainability of treatment systems. This paper presents a broader view on the possible applications of anaerobic treatment systems not only for organic matter removal but also for resources recovery aiming at the improvement of the sustainability of DST.     

生活污水分散处理技术的进展

为了确保我国水体清洁,生活污水除了集中处理之外,分散式的净化槽系统也是不可缺少的。对生活污水分散处理的特点、难点及发展状况进行了论述,探讨了生活污水分散处理技术在应用中存在的问题及解决方法,指出厌氧和好氧生物膜联合处理的小型一体化生活污水净化槽的发展方向。     

The Role of Particulate Organic Matter and Acetic Acid in the Removal of Phosphate in Anaerobic/Aerobic Activated Sludge Processes

Acetic acid is thought to be an important substrate for the removal of phosphate in anaerobic/aerobic activated sludge (AS) processes. However, the acetic acid content in municipal sewage is low, and the main organic compounds in such sewage are particulate organic matters (POM) that are converted to endogenous substrates (E(ntrapped) POM, i.e., EPOM) in AS processes. Thus, the question arises whether it is really acetate or POM, which is important for the removal of phosphate in full‐scale AS plants. AS was harvested from a full‐scale anaerobic/aerobic AS plant. The amount of phosphate released after the addition of acetic acid depends on the AS conditions, particularly the influent sewage quality. However, the amount of phosphate released by EPOM was not affected by the AS conditions, and the amount of phosphate released per AS concentration and per unit of time was calculated to be about 0.86 mg PO₄‐P/g MLSS/hour. When the AS concentration is 2.5 g/L and the mixed‐liquor retention time is 2 hours in the anaerobic zone, about 4 mg/L PO₄‐P is released from EPOM. Under these conditions, phosphate in such sewage is removed by full‐scale AS plants without using acetic acid. In the case of carbon deficiency, the introduction of primary sludge to the anaerobic zone promoted the release of phosphate.     

Synthesis of intracellular storage polymers by Amaricoccus kaplicensis, a tetrad forming bacterium present in activated sludge

AIMS: The study investigated the physiology of Amaricoccus kaplicensis to determine whether it could outcompete polyphosphate accumulating bacteria in activated sludge systems removing phosphorus, by preferentially assimilating substrates in the anaerobic stages of these processes. METHODS AND RESULTS: The storage processes were investigated under anaerobic, anoxic and aerobic conditions in both batch and periodically fed cultures in an aerobic sequencing batch reactor (SBR). Amaricoccus kaplicensis showed a high capacity for storing aerobically large amounts of acetate as poly beta-hydroxybutyrate (PHB) at high rates. However, no acetate assimilation under anaerobic conditions and very slow assimilation under anoxic conditions could be detected. CONCLUSION: Amaricoccus kaplicensis in pure culture does not behave as polyphosphate accumulating bacteria competitor; therefore it is difficult to understand why anaerobic/aerobic systems often contain such large numbers of Amaricoccus cells. SIGNIFICANCE AND IMPACT OF THE STUDY: Amaricoccus kaplicensis is probably not responsible for the failure of activated sludge systems removing phosphorus, and other organisms capable of anaerobic substrate assimilation should be sought.     

The sulfate-reducing capacity of bacteria in the genus Pseudomonas]

Active sulphate-reducing microorganism which belongs to the genus Pseudomonas has been distinguished and described. The culture is a facultative aerobe, optimum Eh is -170-180 mV. Pseudomonas sp. being cultivated under strictly anaerobic conditions sulphate-reduction proceeds more intensively than under aerobic conditions. This fact should be taken into account under treatment of industrial sewage.     

A Remark on Microorganisms in Lake Sediments with Emphasis on Polyphosphate-accumulating Bacteria

Bacteria which are able to store large amounts of phosphorus as polyphosphate (PP) under aerobic conditions and to release it under anaerobic conditions are utilized for the advanced treatment of sewage. This note presents some results which indicate that PP-accumulating bacteria which possibly participate in the immobilization and release of dissolved phosphate may also be present in lake sediments.     

Pyrimidine dimer excision repair of DNA in Bacteroides fragilis wild-type and mitomycin C-sensitive/UV-sensitive mutants

An enzyme preparation purified from Micrococcus luteus was shown to be specific for UV-induced pyrimidine dimers and was suitable for the detection of DNA excision repair systems. The wild-type Bacteroides fragilis Bf-2 strain and a mitomycin C-sensitive mutant (MTC25) had constitutive dimer excision systems which functioned efficiently under anaerobic and aerobic conditions. A UV-sensitive mutant (UVS9) had markedly reduced levels of the constitutive dimer excision systems under anaerobic and aerobic conditions. Since liquid holding recovery under aerobic conditions was inhibited by chloramphenicol whereas the final level of excision repair in B. fragilis Bf-2 was not affected, it is concluded that pyrimidine dimer removal is not the process responsible for increased physiological aerobic liquid holding recovery.     

Fate of linear alkylbenzene sulfonates in the environment: A review

The fate and risk of linear alkylbenzene sulfonates (LAS) in various compartments of the environment have been reviewed. Under aerobic conditions LAS degrade rapidly and concentration of LAS has been found very low in effluents from aerobic sewage treatment plants (STP). On the contrary, in anaerobic STPs effluents, LAS concentrations have been found very high. Anaerobic effluents containing high LAS concentrations have been found to pose risk to aquatic environment. Similarly, LAS concentrations have been found high in anaerobically treated sewage sludge's. LAS enter the soil as a result of sludge application to the land. Risk to aquatic and terrestrial ecosystems is increased when wastewaters and sludge's are treated anaerobically.     

High efficiency of a coupled aerobic-anaerobic recycling biofilm reactor system in the degradation of recalcitrant chloroaromatic xenobiotic compounds

Chloroaromatic compounds are xenobiotics that cause great concern. The degradation of a model molecule, 3,4-dichlorobenzoate (3,4-DCB), was studied using three aerobic (AE)-anaerobic (AN) biofilm reactor systems: a coupled aerobic-anaerobic recycle biofilm reactor (CAR) system, an in-series anaerobic-aerobic biofilm reactor (SAR) system; and an independent aerobic and anaerobic biofilm reactor (IAR) system. In all three systems the inlet substrate concentration was 2.0 g/l and the dilution rates ranged from 0.045 to 0.142 per hour. The results show that the degradation efficiency of the CAR system (expressed as dechlorination and xenobiotic disappearance efficiencies, and biomass yield), was higher at all dilution rates tested than in both SAR and IAR systems. Moreover, dechlorination and xenobiotic disappearance efficiencies for resting suspended aerobic and anaerobic cells or mixed aerobic-anaerobic growing cells under anaerobic conditions were higher than under aerobic conditions. These results suggest that a “cooperative metabolism” between aerobic and anaerobic bacteria (caused by an exchange of cells and metabolites between AE and AN reactors) in the CAR system overcame the metabolic and kinetic limitations of aerobic and anaerobic bacteria in the AE and AN reactors of IAR and SAR systems. Therefore, the degradation efficiency of persistent and recalcitrant chloroaromatic xenobiotic compounds could be enhanced by using a CAR system. Received: 1 March 1999 / Received revision: 11 May 1999 / Accepted: 16 May 1999     

Nitrogen removal in an anaerobic baffled filter reactor with aerobic post-treatment

A new sewage treatment system was studied, which consisted of an anaerobic baffled filter reactor and the following aerobic post-treatment. One of the two studied systems (AN-I) was inoculated with psychrophilic digested sludge, the second one (AN-II) was operated without inoculation. The HRT in anaerobic and aerobic parts of the reactors were about 15 and 4 h, respectively. The temperature in both reactors varied during the year from 4.5 to 23 degrees C. All monitored parameters were removed with relatively high efficiencies (COD = 78.6-83.0%, BOD5 = 92.5-94.0% and SS = 80.9-92.7%). An intensive nitrification process was observed during the whole year in both reactors (under average temperature of 5.9 degrees C in January 2000, also). The average removal of the NH4-N varied during the year from 46.4% to 87.3%. In both systems a partial denitrification process was observed, too.     

Distribution of Bdellovibrio bacteriovorus in sewage works, river water, and sediments.

Bdellovibrio was found in all liquid phases of the sewage works examined. The predator was also found in all the river sediments and sewage-polluted river waters examined but could not be found in some unpolluted river waters. Bdellovibrio was able to multiply on the high numbers of bacteria present in the aerobic percolating filter film but could not survive in anaerobic sludge. Similarly, the predator was present in the aerobic surface layers of river sediments but not in the anaerobic bottom layers. The major source of Bdellovibrio in the polluted rivers examined were sewage works effluents, and numbers in both river water and sediment were correlated with river water quality. It was unlikely that Bdellovibrio was important in reducing numbers of other bacteria in either sewage or river sediment.     

Distribution of Bdellovibrio bacteriovorus in sewage works, river water, and sediments.

Bdellovibrio was found in all liquid phases of the sewage works examined. The predator was also found in all the river sediments and sewage-polluted river waters examined but could not be found in some unpolluted river waters. Bdellovibrio was able to multiply on the high numbers of bacteria present in the aerobic percolating filter film but could not survive in anaerobic sludge. Similarly, the predator was present in the aerobic surface layers of river sediments but not in the anaerobic bottom layers. The major source of Bdellovibrio in the polluted rivers examined were sewage works effluents, and numbers in both river water and sediment were correlated with river water quality. It was unlikely that Bdellovibrio was important in reducing numbers of other bacteria in either sewage or river sediment.     

Substrate utilization kinetic model for biological treatment process

The applicability of Contois' kinetic equation to aerobic and anaerobic treatments of organic wastes is investigated. A refractory coefficient to account for the nonbiodegradable portion of the organic substrates in the digester is incorporated into the kinetic equation. The kinetic equation is applied to the data for aerobic digestions of organic substrates and for anaerobic treatment of dairy wastes. They all show a very good fit of the kinetic equation to the data. Furthermore, the kinetic parameters and the refractory coefficients are shown to be independent of influent organic substrate concentration. This study confirms previous reports that the effluent quality of biological treatment systems for organic wastes depends on influent organic waste concentration. The effect of temperature on the kinetic parameters and the refractory coefficient for anaerobic treatment of sewage sludge are studied. It shows that the kinetic parameters vary with temperature, while the refractory coefficient remains fairly constant. Equations to predict biodegradable treatment efficiency and volumetric substrate utilization rate are also briefly discussed.     

Effect of oxygen on survival of faecal pollution indicators in drinking water

AIMS: The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water. METHODS AND RESULTS: Aerobic and anaerobic drinking water microcosms were inoculated with E. coli ATCC 25922 or raw sewage. Survival of E. coli was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. coli in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. coli. CONCLUSIONS: The results indicate that oxygen is a major regulator of the survival of E. coli in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. coli may persist longer in drinking water under anaerobic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.     

Microbial degradation of chlorinated phenols

Chlorophenols have been introduced into the environment through their use as biocides and as by-products of chlorine bleaching in the pulp and paper industry. Chlorophenols are subject to both anaerobic and aerobic metabolism. Under anaerobic conditions, chlorinated phenols can undergo reductive dechlorination when suitable electron-donating substrates are available. Halorespiring bacteria are known which can use both low and highly chlorinated congeners of chlorophenol as electron acceptors to support growth. Many strains of halorespiring bacteria have the capacity to eliminate ortho-chlorines; however only bacteria from the species Desulfitobacterium hafniense (formerly frappieri) can eliminate para- and meta-chlorines in addition to ortho-chlorines. Once dechlorinated, the phenolic carbon skeletons are completely converted to methane and carbon dioxide by other anaerobic microorganisms in the environment. Under aerobic conditions, both lower and higher chlorinated phenols can serve as sole electron and carbon sources supporting growth. The best studied strains utilizing pentachlorophenol belong to the genera Mycobacterium and Sphingomonas. Two main strategies are used by aerobic bacteria for the degradation of chlorophenols. Lower chlorinated phenols for the most part are initially attacked by monooxygenases yielding chlorocatechols as the first intermediates. On the other hand, polychlorinated phenols are converted to chlorohydroquinones as the initial intermediates. Fungi and some bacteria are additionally known that cometabolize chlorinated phenols.     

Enhanced biodegradation of cyclotetramethylenetetranitramine (HMX) under mixed electron-acceptor condition

The biodegradation of cyclotetramethylenetetranitramine, commonly known as 'high melting explosive' (HMX), under various electron-acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that the HMX was biodegraded under sulfate reducing, nitrate reducing, fermenting, methanogenic, and mixed electron accepting conditions. However, the rates of degradation varied among the various conditions studied. The fastest removal of HMX (from 22 ppm on day 0 to < 0.05 ppm on day 11) was observed under mixed electron-acceptor conditions, followed in order by sulfate reducing, fermenting, methanogenic, and nitrate reducing conditions. Under aerobic conditions, HMX was not biodegraded, which indicated that HMX degradation takes place under anaerobic conditions via reduction. HMX was converted to methanol and chloroform under mixed electron-acceptor conditions. This study showed evidence for HMX degradation under anaerobic conditions in a mixed microbial population system similar to any contaminated field sites, where a heterogeneous population exists.     

Acetylene Reduction (Nitrogen Fixation) by Pulp and Paper Mill Effluents and by Klebsiella Isolated from Effluents and Environmental Situations

High rates of acetylene (C₂H₂) reduction (nitrogenase activity) were observed in woodroom effluent from a neutral sulfite semi-chemical mill under aerobic (up to 644 nmol of C₂H₄ produced per ml per h) and under anaerobic (up to 135 nmol of C₂H₄ produced per ml per h) conditions. Pasteurized effluent developed C₂H₂ reduction activity when incubated under anaerobic but not under aerobic conditions. Activities were increased by addition of 0.5 to 3.0% glucose or xylose. Enrichment and enumeration studies showed that N₂-fixing Azotobacter and Klebsiella were abundant, and N₂-fixing Bacillus was present. Of 129 isolates of Klebsiella from pulp mills, lakes, rivers, and drainage and sewage systems, 32% possessed nitrogen-fixing ability.     

Sequential anaerobic/aerobic biodegradation of chloroethenes--aspects of field application

Because of a range of different industrial activities, sites contaminated with chloroethenes are a world-wide problem. Chloroethenes can be biodegraded by reductive dechlorination under anaerobic conditions as well as by oxidation under aerobic conditions. The tendency of chloroethenes to undergo reductive dechlorination decreases with a decreasing number of chlorine substituents, whereas with less chlorine substituents chloroethenes more easily undergo oxidative degradation. There is currently a growing interest in aerobic metabolic degradation of chloroethenes, which demonstrates advantages compared to cometabolic degradation pathways. Sequential anaerobic/aerobic biodegradation can overcome the disadvantages of reductive dechlorination and leads to complete mineralization of the chlorinated pollutants. This approach shows promise for site remediation in natural settings and in engineered systems.     

Fermentative and oxidative transformation of ferulate by a facultatively anaerobic bacterium isolated from sewage sludge.

A facultatively anaerobic, gram-negative, non-sporeforming, motile rod-shaped bacterium was isolated from methanogenic consortia degrading 3-methoxy-4-hydroxycinnamate (ferulate). Consortia were originally enriched from a laboratory anaerobic digester fed sewage sludge. In the absence of exogenous electron acceptors and with the addition of 0.1% yeast extract, the isolated bacterium transformed ferulate under strictly anaerobic conditions (N2-CO2 gas phase). Ferulate (1.55 mM) was demethoxylated and dehydroxylated with subsequent reduction of the side chain, resulting in production of phenylpropinate and phenylacetate. Under aerobic conditions, the substrate was completely degraded, with transient appearance of caffeate as the first aromatic intermediate and beta-ketoadipate as an aliphatic intermediate. The pure culture has been tentatively assigned to the genus Enterobacter with the type strain DG-6 (ATCC 35929). Tentative pathways for both fermentative and oxidative degradation of ferulate are now proposed.