The effect of pH on N2O production under aerobic conditions in a partial nitritation system

Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N₂O) emissions during nitrogen transformation. N₂O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55 ± 5% conversion of the 1 g NH₄⁺-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N₂O emission factor was 1.0 ± 0.1% of the ammonium converted. pH was shown to have a major impact on the N₂O production rate of the AOB enriched culture. In the investigated pH range of 6.0-8.5, the specific N₂O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15 ± 0.01 mg N₂O-N/h/g VSS, but increased with pH to a maximum of 0.53 ± 0.04 mg N₂O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N₂O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N₂O production. The N₂O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5-78 mg NH₃-N/L and 0.15-4.6 mg HNO₂-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations.     

Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants

International guidance for estimating emissions of the greenhouse gas, nitrous oxide (N₂O), from biological nutrient removal (BNR) wastewater systems is presently inadequate. This study has adopted a rigorous mass balance approach to provide comprehensive N₂O emission and formation results from seven full-scale BNR wastewater treatment plants (WWTP). N₂O formation was shown to be always positive, yet highly variable across the seven plants. The calculated range of N₂O generation was 0.006-0.253 kgN₂O-N per kgN denitrified (average: 0.035 ± 0.027). This paper investigated the possible mechanisms of N₂O formation, rather than the locality of emissions. Higher N₂O generation was shown to generally correspond with higher nitrite concentrations, but with many competing and parallel nitrogen transformation reactions occurring, it was very difficult to clearly identify the predominant mechanism of N₂O production. The WWTPs designed and operated for low effluent TN (i.e. <10 mgN L⁻¹) had lower and less variable N₂O generation factors than plants that only achieved partial denitrification.     

N2O emission from a partial nitrification-anammox process and identification of a key biological process of N2O emission from anammox granules

Emission of nitrous oxide (N₂O) during biological wastewater treatment is of growing concern. The emission of N₂O from a lab-scale two-reactor partial nitrification (PN)-anammox reactor was therefore determined in this study. The average emission of N₂O from the PN and anammox process was 4.0 ± 1.5% (9.6 ± 3.2% of the removed nitrogen) and 0.1 ± 0.07% (0.14 ± 0.09% of the removed nitrogen) of the incoming nitrogen load, respectively. Thus, a larger part (97.5%) of N₂O was emitted from the PN reactor. The total amount of N₂O emission from the PN reactor was correlated to nitrite (NO₂⁻) concentration in the PN effluent rather than DO concentration. In addition, further studies were performed to indentify a key biological process that is responsible for N₂O emission from the anammox process (i.e., granules). In order to characterize N₂O emission from the anammox granules, the in situ N₂O production rate was determined by using microelectrodes for the first time, which was related to the spatial organization of microbial community of the granule as determined by fluorescence in situ hybridization (FISH). Microelectrode measurement revealed that the active N₂O production zone was located in the inner part of the anammox granule, whereas the active ammonium consumption zone was located above the N₂O production zone. Anammox bacteria were present throughout the granule, whereas ammonium-oxidizing bacteria (AOB) were restricted to only the granule surface. In addition, addition of penicillin G that inhibits most of the heterotrophic denitrifiers and AOB completely inhibited N₂O production in batch experiments. Based on these results obtained, denitrification by putative heterotrophic denitrifiers present in the inner part of the granule was considered the most probable cause of N₂O emission from the anammox reactor (i.e., granules).     

Biodegradation of phytosanitary products in biological wastewater treatment

Agricultural activity generates two types of waste: firstly, biodegradable organic effluents generally treated by biological processes and, secondly, phytosanitary effluents which contain residues of plant protection products. The latter are collected and treated. Current technological solutions are essentially based on concentration or physical-chemical processes. However, recent improvements in the biodegradability of pesticides open the way to the consideration of alternative, biological, treatment using mixed liquor from wastewater plant activated sludge. The feasibility of the biological treatment of viticultural effluents has been evaluated by the application of pesticides to activated sludge. The necessity for selection of a pesticide-resistant biomass has been highlighted. The elimination of the phytosanitary products shows the potential of a resistant biomass in the treatment of pesticides. The aerated biological storage ponds at three wineries, followed by a sand or reed-bed filter, were used for the treatment of the total annual volume of the viticulture effluents and validate the laboratory experiments. The results show that the biological purification of pesticides by activated sludge is possible by allowing approximately 8 days for biomass adaptation. Stability of purification occurs between 20 and 30 days.     

Biodegradability enhancement of a pesticide-containing bio-treated wastewater using a solar photo-Fenton treatment step followed by a biological oxidation process

This work proposes an efficient combined treatment for the decontamination of a pesticide-containing wastewater resulting from phytopharmaceutical plastic containers washing, presenting a moderate organic load (COD = 1662-1960 mg O₂ L⁻¹; DOC = 513-696 mg C L⁻¹), with a high biodegradable organic carbon fraction (81%; BOD₅ = 1350-1600 mg O₂ L⁻¹) and a remaining recalcitrant organic carbon mainly due to pesticides. Nineteen pesticides were quantified by LC-MS/MS at concentrations between 0.02 and 45 mg L⁻¹ (14-19% of DOC). The decontamination strategy involved a sequential three-step treatment: (a) biological oxidation process, leading to almost complete removal of the biodegradable organic carbon fraction; (b) solar photo-Fenton process using CPCs, enhancing the bio-treated wastewater biodegradability, mainly due to pesticides degradation into low-molecular-weight carboxylate anions; (c) and a final polishing step to remove the residual biodegradable organic carbon, using a biological oxidation process. Treatment performance was evaluated in terms of mineralization degree (DOC), pesticides content (LC-MS/MS), inorganic ions and low-molecular-weight carboxylate anions (IC) concentrations. The estimated phototreatment energy necessary to reach a biodegradable wastewater, considering pesticides and low-molecular-weight carboxylate anions concentrations, Zahn-Wellens test and BOD₅/COD ratio, was only 2.3 kJ_UV L⁻¹ (45 min of photo-Fenton at a constant solar UV power of 30 W m⁻²), consuming 16 mM of H₂O₂, which pointed to 52% mineralization and an abatement higher than 86% for 18 pesticides. The biological oxidation/solar photo-Fenton/biological oxidation treatment system achieved pesticide removals below the respective detection limits and 79% mineralization, leading to a COD value lower than 150 mg O₂ L⁻¹, which is in agreement with Portuguese discharge limits regarding water bodies.     

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination--a review

Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.     

Application of O3/UV/H2O2 oxidation and process optimization for treatment of potato chips manufacturing wastewater

Effluents coming from potato chips manufacturing have high organic loads and require adequate treatment before discharge to environment. In this study, O₃/UV/H₂O₂ advanced oxidation process was applied to treat these wastewaters. With this aim, batch experiments were conducted in a reaction tank equipped with ozone injection and UV irradiation. Process variables were determined to be pH, ozone concentration, reaction time, H₂O₂ dosage and efficiency of the system was evaluated considering total organic carbon (TOC) removal. Central composite design technique was applied to examine the individual and synergetic effects of the experimental factors. A quadratic model was developed to maximize the TOC removal. Furthermore, operation costs were calculated for different experimental conditions and interactions between process variables and costs were analysed.     

生物活性炭（BAC）技术在废水处理中的应用与研究

总结了生物活性炭技术在废水处理和污水再生利用处理中的应用,并进一步阐述了生物活性炭对污染物的去除机理,归纳了生物活性炭技术在水处理中的优势,以推广生物活性炭技术的应用.     

废水生物处理中细胞生长动力学模型及其运用

从细胞生长的Monod方程式出发,讨论了基于Monod方程的细胞生长动力学在废水生物处理过程模拟中的修正、拓展,对废水生物处理过程模拟中Monod方程的运用进行了梳理。     

Influence of wastewater treatment on sludge production and processing

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery.     

A chemically enhanced biological process for lowering operative costs and solid residues of industrial recalcitrant wastewater treatment

An innovative process based on ozone-enhanced biological degradation, carried out in an aerobic granular biomass system (SBBGR - Sequencing Batch Biofilter Granular Reactor), was tested at pilot scale for tannery wastewater treatment chosen as representative of industrial recalcitrant wastewater. The results have shown that the process was able to meet the current discharge limits when the biologically treated wastewater was recirculated through an adjacent reactor where a specific ozone dose of 120 mg O₃/L_influent was used. The benefits produced by using ozone were appreciable even visually since the final effluent of the process looked like tap water. In comparison with the conventional treatment, the proposed process was able to reduce the sludge production by 25-30 times and to save 60% of operating costs.Molecular in situ detection methods were employed in combination with the traditional measurements (oxygen uptake rate, total protein content, extracellular polymeric substances and hydrophobicity) to evaluate microbial activity and composition, and the structure of the biomass. A stable presence of active bacterial populations was observed in the biomass with the simultaneous occurrence of distinctive functional microbial groups involved in carbon, nitrogen and sulphate removal under different reaction environments established within the large microbial aggregates. The structure and activity of the biomass were not affected by the use of ozone.     

Solar-based detoxification of phenol and p-nitrophenol by sequential TiO2 photocatalysis and photosynthetically aerated biological treatment

Simulated solar UV/TiO(2) photocatalysis was efficient to detoxify a mixture of 100 mgphenoll(-1) and 50 mgp-nitrophenol (PNP) l(-1) and allow the subsequent biodegradation of the remaining pollutants and their photocatalytic products under photosynthetic aeration with Chlorella vulgaris. Photocatalytic degradation of phenol and PNP was well described by pseudo-first order kinetics (r(2)>0.98) with removal rate constants of 1.9x10(-4) and 2.8x10(-4)min(-1), respectively, when the pollutants were provided together and 5.7x10(-4) and 9.7x10(-4)min(-1), respectively, when they were provided individually. Photocatalytic pre-treatment of the mixture during 60 h removed 50+/-1% and 62+/-2% of the phenol and PNP initially present but only 11+/-3% of the initial COD. Hydroquinone, nitrate and catechol were identified as PNP photocatalytic products and catechol and hydroquinone as phenol photocatalytic products. Subsequent biological treatment of the pre-treated samples removed the remaining contaminants and their photocatalytic products as well as 81-83% of the initial COD, allowing complete detoxification of the mixture to C. vulgaris. Similar detoxification efficiencies were recorded after biological treatment of the irradiated mixture with activated sludge microflora or with an acclimated consortia composed of a phenol-degrading Alcaligenes sp. and a PNP-degrading Arthrobacter sp., although the acclimated strains biodegraded the remaining pollutants faster. Biological treatment of the non-irradiated mixture was inefficient due to C. vulgaris inhibition.     

Assessment of activated sludge microbial community analysis in full-scale biological wastewater treatment plants using patterns of fatty acid isopropyl esters (FAPEs)

This investigation introduces the application of a relatively rapid technique to obtain information about the dynamic nature of microbial communities in activated sludge. The objective has been to consider variability due to measurement errors and protocol changes within the same quantitative framework as the analysis of systematic differences in microbial communities in large-scale aerobic activated sludge secondary wastewater treatment systems. Adjustments to the methodology were considered due to their potential for simplifying and shortening the analysis procedure. All modifications to the protocols used to assay the composition of microbial fatty acids (MFAs) of activated sludge imposed some bias to the chromatographic data. This methodological bias was similar in magnitude to the level of discrimination between activated sludge microbial community structures that were considered as part of the present study. MFA analysis supported the expectations of subtle but systematic community structure differences and shifts in activated sludge based on the current understanding of these wastewater treatment systems. A standardized MFA methodology was shown to be sensitive to minor systematic changes in activated sludge communities due the anticipated underlying factors of selective pressures from the process configuration, history, operational conditions and/or nutrient status. The chemometric approach of fatty acid isopropyl ester analysis of activated sludge can provide a routine tool for meaningful and quantitative information of changes in activated sludge quality in full-scale treatment systems.     

纺织污水处理厂厌氧水解及接触氧化工艺调试

介绍了空港经济区纺织污水处理厂＂厌氧水解＋接触氧化＋化学混凝法＋沉淀分离＂组合工艺的运行调试过程,针对纺织废水水质间歇性超标、水质波动大以及纺织废水与市政污水的比例波动等问题,通过合理调整气水比、溶解氧、生物膜厚度、加药量等工艺参数,使系统的出水水质达到了设计要求,可为同行业污水处理厂的试运行调试提供参考。     

Dynamics of nitric oxide and nitrous oxide emission during full-scale reject water treatment

Emission of NO and N2O from a full-scale two-reactor nitritation-anammox process was determined during a measurement campaign at the Dokhaven-Sluisjesdijk municipal WWTP (Rotterdam, NL). The NO and N2O levels in the off-gas responded to the aeration cycles and the aeration rate of the nitritation reactor, and to the nitrite and dissolved oxygen concentration. Due to the strong fluctuations in the NO and N2O levels in both the nitritation and the anammox reactor, only time-dependent measurements could yield a reliable estimate of the overall NO and N2O emissions. The NO emission from the nitritation reactor was 0.2% of the nitrogen load and the N2O emission was 1.7%. The NO emission from the anammox reactor was determined to be 0.003% of the nitrogen load and the N2O emission was 0.6%. Emission of NO2 could not be detected from the nitritation-anammox system. Denitrification by ammonia-oxidizing bacteria was considered to be the most probable cause of NO and N2O emission from the nitritation reactor. Since anammox bacteria have not been shown to produce N2O under physiological conditions, it is also suspected that ammonia-oxidizing bacteria contribute most to N2O production in the anammox reactor. The source of NO production in the anammox reactor can be either anammox bacteria or denitrification by heterotrophs or ammonia-oxidizing bacteria. Based on the results and previous work, it seems that a low dissolved oxygen or a high nitrite concentration are the most likely cause of elevated NO and N2O emission by ammonia-oxidizing bacteria. The emission was compared with measurements at other reject water technologies and with the main line of the Dokhaven-Sluisjesdijk WWTP. The N2O emission levels in the reject water treatment seem to be in the same range as for the main stream of activated sludge processes. Preliminary measurements of the N2O emission from a one-reactor nitritation-anammox system indicate that the emission is lower than in two-reactor systems.     

Partial wet oxidation of p-coumaric acid: Oxidation intermediates, reaction pathways and implications for wastewater treatment

p-Coumaric acid is representative of the polyphenolic fraction typically found in olive oil processing and wine-distillery wastewaters. The batch oxidation of p-coumaric acid has been investigated using a high-pressure reactor at temperatures varying from 403 to 523 K and pressures from 3 to 7 MPa. Concentrations of reaction intermediates were determined as a function of oxidation time using High Performance Liquid Chromatography (HPLC) as the main analytical technique, and an oxidation mechanism for p-coumaric acid is suggested. The results are discussed with respect to developing an integrated chemical-biological treatment process for organic wastewater.     

Removal of pharmaceuticals and fragrances in biological wastewater treatment

The removal of seven pharmaceuticals and two fragrances in the biological units of various full-scale municipal wastewater treatment plants was studied. The observed removal of pharmaceuticals was mainly due to biological transformation and varied from insignificant (<10%, carbamazepine) to>90% (ibuprofen). However, no quantitative relationship between structure and activity can be set up for the biological transformation. Overall, it can be concluded that for compounds showing a sorption coefficient (K(d)) of below 300 L kg(-1), sorption onto secondary sludge is not relevant and their transformation can consequently be assessed simply by comparing influent and effluent concentrations. The two fragrances (HHCB, AHTN) studied were mainly removed by sorption onto sludge. For the compounds studied, comparable transformation and sorption was seen for different reactor types (conventional activated sludge, membrane bioreactor and fixed bed reactor) as well as for sludge ages between 10 and 60-80 days and temperatures between 12 degrees C and 21 degrees C. However, some significant variations in the observed removal currently lack an explanation. The observed incoming daily load of iopromide and roxithromycin in medium-sized municipal wastewater treatment plants (up to 80,000 population equivalents) is generated by only a small number of patients: the consequences for representative 24h composite sampling are discussed. Generally, the paper presents a method for setting up mass balances for micropollutants over entire wastewater treatment plants, including an estimation of the accuracy of the quantified fate (i.e. removal by sorption and biological transformation).     

废水处理过程中异常问题的解析与控制

以某纺织污水处理厂为实例，对运行过程中生物接触氧化单元出现的生物膜过厚、生物膜发白和红斑瓢体虫大量爆发的问题进行了解析，并提出了相应的对策和控制措施，不仅解决了实际问题，还可为国内其他污水处理厂提供指导。     

膨润土的改性研究及在污水治理中的应用

介绍了蒙脱石的结构和基本性质 ,对近年来我国膨润土的活化、改性技术如焙烧活化、酸活化、无机改性、有机改性、交联膨润土的合成和改性机理及改性效果进行了归纳总结。活化改性改善了蒙脱石的微观结构 ,提高了膨润土的吸附能力和离子交换能力 ;对改性膨润土在污水治理中的应用进行了综述。改性膨润土可去除水体中的重金属离子、芳香族化合物、有毒难生物降解有机物 ,还具有脱色、脱磷、除臭等作用。给出了改性膨润土去除水中重金属离子、有机污染物的机理。指出了膨润土在污水处理中存在的问题 ,并展望其应用前景 ,认为膨润土是一种很有前途的污水处理材料。