Effect of sludge recycle on performance of a rotating biodisc contactor treating saline wastewater

A rotating biodisc contactor (RBC) was used for biological treatment of synthetic saline wastewater with and without sludge (cell) recycle. Synthetic wastewater composed of diluted molasses, urea, KH_zPO₄, MgSO₄ and 3% salt (NaCl) was fed to the RBC unit with different flow rates. Underflow from a sedimentation tank placed at the end of RBC unit was recycled to the RBC unit with a constant flow rate. COD removal rates and efficiencies were determined for the cases of with and without sludge recycle and compared. COD removal efficiencies and rates obtained with sludge recycle were higher than those obtained without sludge recycle at low A/Q ratios (high flow rate) because of extra residence time provided by sedimentation tank. However, no significant difference was observed in the performance of RBC with and without sludge recycle at high A/Q ratios (low flow rates). Because of poor sedimentation characteristics of the culture no significant increase in biomass concentration in the RBC was observed when the system was operated with sludge recycle.     

Short-term batch studies on biological removal of chromium from synthetic wastewater using activated sludge biomass

Biological treatment of Cr(VI)-containing wastewater has drawn much attention recently as a method to treat environmental Cr(VI) contamination. The activated sludge method, due to its convenient operation and easy-to-scale-up, has been widely applied to treat municipal wastewater and some industrial wastewaters. In order to develop a suitable technique using activated sludge as the biomass to continuously remove Cr(VI) from wastewater, this paper investigated in short-term batch experiments the environmental elements affecting chromium biological removal from synthetic wastewater. The dissolved oxygen (DO), Cr(VI) initial concentration, biomass density, temperature, glucose content in the influent and contact time were observed to strongly influence chromium removal. It was found that the chromium removal efficiency decreased with the increase of DO and Cr(VI) initial concentration as well as glucose content in the feed, but increases in temperature and contact time improved the chromium removal efficiency. Although raising biomass concentration resulted in an increased chromium removal efficiency under both anaerobic and aerobic conditions, its influence on specific chromium removal was not significant.     

Enhancing denitrification using a carbon supplement generated from the wet oxidation of waste activated sludge

This study compared the effect of four pure carbon supplements on biological denitrification to a liquor derived as a by-product from the wet oxidation (WO) of waste activated sludge. Sequencing batch reactors were used to acclimate sludge biomass, which was used in batch assays. Acetate, WO liquor and ethanol-supplementation generated the fastest denitrification rates. Acetate and WO liquor were efficiently utilised by all acclimated biomass types, while poor rates were achieved with methanol and formate. When comparing an inoculum from an ethanol-supplemented and non-supplemented wastewater treatment plant (WWTP), the ethanol-acclimated sludge obtained superior denitrification rates when supplemented with ethanol. Similarly high nitrate removal rates were achieved with both sludge types with acetate and WO liquor supplementation, indicating that WO liquors could achieve excellent rates of nitrate removal. The performance of the WO liquor was attributed to the variety of organic carbon substrates (particularly acetic acid) present within the liquor.     

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH₃–N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60–70% for total nitrogen by SND with HRT of 4–6 h, and the concentrations of NH₃–N and TN in effluent are less than 5 and 15 mg/L, respectively.     

Simultaneous removal of carbon and nitrogen from municipal-type synthetic wastewater using net-like rotating biological contactor (NRBC)

The treatment of municipal-type synthetic wastewater was carried out using a three stages net-like rotating biological contactor (NRBC). The results indicated that, compared with conventional rotating biological contactor (RBC), NRBC have several advantages, such as quick start-up, high biomass concentration and can handle high organic loading rates. The COD and total nitrogen removal rates achieved were 78.8–89.7% and 40.2–61.4%, respectively, in aerobic treatment of low COD municipal-type wastewater at hydraulic retention times (HRT) from 5 to 9 h. The COD removal rate achieved 80–95% when organic loading varied between 16 and 40 gCOD/m² d. A large amount of nematodes were found in the NRBC system, which made the NRBC system produce relatively low amounts of waste sludge, due to their grazing.     

Enhancing nitrogen removal in an Orbal oxidation ditch by optimization of oxygen supply: practice in a full-scale municipal wastewater treatment plant

Seven different aeration modes, in which oxygen supply was changed by adjusting the number of aerators, were designed and applied in a full-scale municipal wastewater treatment plant with Orbal oxidation ditch to investigate the influence of dissolved oxygen (DO) on nitrogen removal performance. The full-scale experiment results of 574 days showed that nitrogen removal efficiency depended on the degree of nitrification and denitrification in the outer channel, which was the largest contributor for TN removal in the Orbal oxidation ditch. Appropriate aeration control in the outer channel was essential to balance nitrification and denitrification in the Orbal oxidation ditch. When DO was as low as about 0.2 mg/L in the outer channel, the highest TN removal efficiency of 75% was obtained. Microbial analysis confirmed that aerobic and anaerobic bacteria coexisted in the outer channel. The greater species diversity and more intensive activities of these bacteria in aeration Mode V may be responsible for the higher TN removal efficiency compared with Mode III. These results suggest that different aerated conditions in the Orbal oxidation ditch might have a significant effect on microbial community characteristics and nitrogen removal efficiencies.     

Kinetic properties of a commercial and a native inoculum for aerobic milk fat degradation

The aerobic fat biodegradation potential and growth characteristics of a commercial and a native inoculum (activated sludge from a dairy wastewater treatment pond), were evaluated. Batch tests were conducted with a medium based on butter oil, as the sole source of carbon, and mineral salts. Residual fat, biomass and CO(2) production were measured. Overall fat removal values were above 78% for both inocula. The growth kinetics of the commercial and native inocula followed Haldane and Monod models respectively. Both inocula showed a similar behaviour when butter oil concentration was under 360 mg/l; at higher values, the difference between the growth rates increased as a consequence of the inhibition exhibited by the commercial inoculum. The selection of an inoculum for bioaugmentation of bioreactors in the wastewater treatment requires a comprehensive knowledge of their degradation ability and tolerance to fluctuating compounds and of the operational conditions that will be utilized.     

Microbial community analysis of three municipal wastewater treatment plants in winter and spring using culture-dependent and culture-independent methods

Low temperatures can result in start-up and operational problems in wastewater treatment plants. The microbial community structures of three full-scale biological processes for municipal wastewater treatment, namely, anoxic-oxic activated sludge (A/O) process, oxidation ditch, and sequencing batch reactor, in winter and spring were investigated. The performances of the three biological processes were all stable during winter and spring. Comparing all three plants, the NH(4) (+)-N removal efficiency using the A/O process was found to be the highest during both winter and spring. According to the similarity coefficient of the polymerase chain reaction and denaturing gradient gel electrophoresis analysis determined via the culture-independent method, the microbial community structure is the most stable using the A/O process at different temperatures. The dominant members primarily belonged to Proteobacteria, Nitrospira, and Bacteroidetes. In addition, Proteobacteria was the dominant member in the activated sludge utilizing peptone, glucose, and fatty acid. Compared with other biological processes, the A/O process was superior at low temperatures based on its pollution removal performance and stable microbial community sturcture.     

A non-structured pseudo-homogeneous model for the activated sludge process

The conventional activated sludge process has been in use for many years for treating wastewater. In this paper a non-structured pseudo-homogeneous model was developed to describe the process. Volume changes as well as the external resistance between the forming flocs and substrate were considered in the model. The kinetic model together with the values of parameters were obtained from the literature. A retention time of 12 hr was found to give over 95% removal of the substrate from the wastewater. Floc diameter, retention time, fraction of biomass recycled, substrate and biomass feed concentration were found to be important factors in the overall efficiency of the treatment process.     

Cultivation and characterization of bacterial isolates capable of degrading pharmaceutical and personal care products for improved removal in activated sludge wastewater treatment

Pharmaceutical and personal care products (PPCPs) discharged with wastewater treatment plant (WWTP) effluents are an emerging surface water quality concern. Biological transformation has been identified as an important removal mechanism during wastewater treatment. The aim of this research was the identification of bacteria with characteristics for potential bioaugmentation to enhance PPCP removal. We report here the cultivation and characterization of bacteria capable of degrading PPCPs to ng/L concentrations. An isolation approach was developed using serial enrichment in mineral medium containing 1 mg/L of an individual PPCP as the sole organic carbon source available to heterotrophs until the original activated sludge inocula was diluted to ~10^?8 of its initial concentration, followed by colony growth on solid R2A agar. Eleven bacteria were isolated, eight that could remove triclosan, bisphenol A, ibuprofen, or 17β-estradiol to below 10 ng/L, one that could remove gemfibrozil to below 60 ng/L, and two that could remove triclosan or E2, but not to ng/L concentrations. Most bacterial isolates degraded contaminants during early growth when grown utilizing rich carbon sources and were only able to degrade the PPCPs on which they were isolated. Seven of the bacterial isolates were sphingomonads, including all the triclosan and bisphenol A degraders and the ibuprofen degrader. The study results indicate that the isolated bacteria may have a positive influence on removal in WWTPs if present at sufficient concentrations and may be useful for bioaugmentation.     

Microbial degradation of triclosan by a novel strain of Dyella sp.

A novel strain capable of degrading triclosan was isolated from the acclimated activated sludge and identified to be Dyella sp. WW1 based on 16S rDNA analysis. The effect of initial concentration of triclosan (0.2, 1, 5, and 10 mg/L), temperature (15, 25, and 35 °C), pH (5, 7, and 9), and additional carbon source on the degradation of triclosan was investigated in a mineral medium. The results showed that Dyella sp. WW1 can use triclosan as sole carbon source and degrade it when initial triclosan concentration was in the range of 0.2–10 mg/L. The optimal condition for Dyella sp. WW1 to degrade triclosan was 15 °C and pH 7. TOC removal efficiency was more than 90%. Dyella sp. WW1 can degrade 3,5-dichloro-4-hydrobenzoic via co-metabolism in the presence of triclosan, but cannot degrade trimethoprim, sulfamethoxazole, carbamazepine, and diclofenac. In the presence of glucose, Dyella sp. WW1 firstly utilized glucose to synthesize the biomass and then degraded triclosan. When triclosan concentration decreased to an extent (1.2 mg/L in this study), Dyella sp. WW1 started to use glucose again. The wastewater components did not significantly affect the activity of Dyella sp. WW1 to degrade triclosan. During the biodegradation process, six metabolite products were identified. Based on the metabolites, two degradation pathways were tentatively proposed. In summary, Dyella sp. WW1 could be used for degrading triclosan in the real wastewater.

     

Sludge minimisation technologies

The treatment and disposal of excess sludge represents a bottleneck of wastewater treatment plants all over the world, due to environmental, economic, social and legal factors. There is therefore a growing interest in developing technologies to reduce the wastewater sludge generation. The goal of this paper is to present the state-of-the-art of current minimisation techniques for reducing sludge production in biological wastewater treatment processes. An overview of the main technologies is given considering three different strategies: The first option is to reduce the production of sludge by introducing in the wastewater treatment stage additional stages with a lower cellular yield coefficient compared to the one corresponding to the activated sludge process (lysis-cryptic growth, uncoupling and maintenance metabolism, predation on bacteria, anaerobic treatment). The second choice is to act on the sludge stage. As anaerobic digestion is the main process in sewage sludge treatment for reducing and stabilising the organic solids, two possibilities can be considered: introducing a pre-treatment process before the anaerobic reaction (physical, chemical or biological pre-treatments), or modifying the digestion configuration (two-stage and temperature-phased anaerobic digestion, anoxic gas flotation). And, finally, the last minimisation strategy is the removal of the sludge generated in the activated sludge plant (incineration, gasification, pyrolysis, wet air oxidation, supercritical water oxidation).     

Adaptation of a freshwater anammox population to high salinity wastewater

For the successful application of anaerobic ammonium oxidation (anammox) in wastewater practice it is important to know how to seed new anammox reactors with biomass from existing reactors. In this study, a new high salinity anammox reactor was inoculated with biomass from a freshwater system. The changes in activity and population shifts were monitored. It was shown that freshwater anammox bacteria could adapt to salt concentrations as high as 30 gl(-1) provided the salt concentration was gradually increased. Higher salt concentrations reversibly inhibited anammox bacteria. The nitrogen removal efficiency and maximum anammox activity of the salt adapted sludge was very similar to the reference freshwater sludge. Fluorescence in situ hybridization analysis revealed that the freshwater anammox species Candidatus "Kuenenia stuttgartiensis" was the dominant in both salt adapted sludge and freshwater sludge. These results show that gradual adaptation may be the key to successful seeding of anammox bioreactors.     

Factors affecting the removal of organic micropollutants from wastewater in conventional treatment plants (CTP) and membrane bioreactors (MBR)

As a consequence of insufficient removal during treatment of wastewater released from industry and households, different classes of organic micropollutants are nowadays detected in surface and drinking water. Among these micropollutants, bioactive substances, e.g., endocrine disrupting compounds and pharmaceuticals, have been incriminated in negative effects on living organisms in aquatic biotope. Much research was done in the last years on the fate and removal of those compounds from wastewater. An important point it is to understand the role of applied treatment conditions (sludge retention time (SRT), biomass concentration, temperature, pH value, dominant class of micropollutants, etc.) for the efficiency of conventional treatment plants (CTP) and membrane bioreactors (MBR) concerning the removal of micropollutants such as pharmaceuticals, steroid- and xeno-estrogens. Nevertheless, the removal rates differ even from one compound to the other and are related to the physico-chemical characteristics of the xenobiotics.     

Development of a fixed-bed anammox reactor with high treatment potential

A plug-flow type anaerobic ammonium oxidation (anammox) reactor was developed using malt ceramics (MC) produced from carbonized spent grains as the biomass carriers for anammox sludge. Partial nitrified effluent of the filtrate from the sludge dehydrator of a brewery company was used as influent to a 20 L anammox reactor using MC. An average volumetric nitrogen removal rate (VNR) of 8.78 kg-N/m³/day was maintained stably for 76 days with 1 h of HRT. In a larger anammox reactor (400 L), an average VNR of 4.84 kg-N/m³/day could be maintained for 86 days during the treatment of low strength synthetic inorganic wastewater. As a result of bacterial community analysis for the 20 L anammox reactor, Asahi BRW1, probably originating from the wastewater collected at Asahi Breweries, was detected as the dominant anammox bacterium. These anammox reactors were characterized by a high NH₄-N removal capacity for low strength wastewater with a short hydraulic retention time.     

铁矿物强化厌氧氨氧化效能及其微生物机制研究进展

自然界中的氮循环与铁循环相互交联,参与氮循环的厌氧氨氧化（anaerobic ammonium oxidation,anammox）菌的生长代谢及活性发挥也与铁元素紧密关联。自然界广泛存在的铁矿物因具有运行成本低廉、稳定性好、二次污染小等优势,在污水处理领域得到广泛应用。在厌氧氨氧化脱氮系统中引入适量铁矿物,不仅有助于促进anammox菌和铁还原菌的富集,提高功能基因丰度和相关酶活性,还可能通过影响污泥浓度、血红素c含量、胞外聚合物含量和颗粒化程度,改善污泥性能和提高厌氧氨氧化系统的稳定性。同时,铁矿物具有促进体系多种氮素转化途径（如anammox、铁自养反硝化、铁氨氧化、异化硝酸盐还原成铵和反硝化）相耦合的潜能,可以提高anammox污水处理系统的总氮去除率。本文基于铁矿物在促进污水生物脱氮方面的良好性能及其在anammox系统中的变化,从脱氮效能、污泥特性、微生物特征及酶活性等方面,系统综述了铁矿物对厌氧氨氧化系统的强化作用机制,并从anammox菌对铁矿物的利用及铁元素的摄取角度展望了后续的研究方向,以期为铁矿物强化厌氧氨氧化系统的实际应用提供理论和技术指导。     

Treatment of high strength distillery wastewater (cherry stillage) by integrated aerobic biological oxidation and ozonation

The performance of integrated aerobic digestion and ozonation for the treatment of high strength distillery wastewater (i.e., cherry stillage) is reported. Experiments were conducted in laboratory batch systems operating in draw and fill mode. For the biological step, activated sludge from a municipal wastewater treatment facility was used as inoculum, showing a high degree of activity to distillery wastewater. Thus, BOD and COD overall conversions of 95% and 82% were achieved, respectively. However, polyphenol content and absorbance at 254 nm (A(254)) could not be reduced more than 35% and 15%, respectively, by means of single biological oxidation. By considering COD as substrate, the aerobic digestion process followed a Contois' model kinetics, from which the maximum specific growth rate of microorganisms (mu(max)) and the inhibition factor, beta, were then evaluated at different conditions of temperature and pH. In the combined process, the effect of a post-ozonation stage was studied. The main goals achieved by the ozonation step were the removal of polyphenols and A(254). Therefore, ozonation was shown to be an appropriate technology to aid aerobic biological oxidation in the treatment of cherry stillage.     

Prediction of effluent pollution level in activated sludge systems II. The effect of recirculation and recirculation ratio

The paper describes substrate removal and biomass production in activated sludge wastewater treatment systems with special attention to the effect of recirculation. Applicability of the models presented is verified experimentally.     

Rapid startup and high rate nitrogen removal from anaerobic sludge digester liquor using a SNAP process

In this study, a single-stage autotrophic nitrogen removal reactor, packed with a novel acrylic fiber biomass carrier material (Biofix), was applied for nitrogen removal from sludge digester liquor. For rapid start-up, conventional activated sludge was added to the reactor soon after the attachment of anammox biomass on the Biofix carriers, which allowed conventional activated sludge to form a protective layer of biofilm around the anammox biomass. The Nitrogen removal efficiency reached 75% within 1 week at a nitrogen loading rate of 0.46 kg-N/m³/day for synthetic wastewater treatment. By the end of the synthetic wastewater treatment period, the maximum nitrogen removal rate had increased to 0.92 kg-N/m³/day at a nitrogen loading rate of 1.0 kg-N/m³/day. High nitrogen removal rate was also achieved during the actual raw digester liquor treatment with the highest nitrogen removal rate being 0.83 kg-N/m³/day at a nitrogen loading rate of 0.93 kg-N/m³/day. The thick biofilm on Biofix carriers allowed anammox bacteria to survive under high DO concentration of 5–6 mg/l resulting in stable and high nitrogen removal performance. FISH and CLSM analysis demonstrated that anammox bacteria coexisted and surrounded by ammonium oxidizing bacteria.     

Biodegradation of wastewater pollutants by activated sludge encapsulated inside calcium-alginate beads in a tubular packed bed reactor

The wastewater treatment plants produce large quantities of biomass (sludge) that require about one-third of the total inversion and operation plant costs for their treatment. By the microorganisms immobilization it is possible to handle high cell concentration in the reactor, increasing its efficiency, reducing the loss of biomass and the wash out is avoided. Moreover, there is no cell growth then the sludge production is reduced. In this study, the COD removal and VSS variation were modeled in a tubular reactor with activated sludge immobilized in Ca-alginate. Moreover, two aspects that are commonly not considered in the performance of the actual reactors of this kind were introduced; the performance in non-steady state and the dispersion effect. The model was calibrated with an actual wastewater taken out from a Mexican wastewater treatment plant. The results of the performance of the tubular bioreactor at different scenarios (i.e., different residence time and VSS in the reactor) are presented. With longer residence times and higher VSS concentration in the Ca-alginate beads in the tubular bioreactor it is possible to increase the time operation of the bioreactor and to treat higher volumes of wastewater. During the process, the sludge generation was drastically reduced and it is possible to remove nitrogen form the wastewater making this process more attractive.