Municipal-treated wastewater reuse for plant nurseries irrigation

Results of an experiment aimed at assessing the possibility of reusing reclaimed wastewater for nursery ornamental plants are presented. Tests were carried out in Pistoia (Italy). A pilot plant for tertiary treatment (filtration and peracetic acid + UV disinfection) of the local wastewater treatment plant (WWTP) effluent was set up. An experimental plot with six containerized ornamental species was irrigated with the tertiary effluent and growth and physiological parameters were monitored. A control plot irrigated with fertigated water (nutrient-enriched groundwater) was also set up in order to compare the plants response to different kinds of irrigation water. The refinery treatment by filtration and disinfection with Peracetic Acid (PAA) and UV together was very effective in bacteria removal. The value of 2 MPN of Total Coliforms in 100 ml set by Italian law (until June 2003) for unrestricted irrigation was constantly satisfied. Agronomic results indicate no major limitations to the use of a tertiary effluent as an irrigation source in an ornamental plant nursery. The nutrient content of the tertiary effluent was able to maintain good plant growth as well as fertigated water for most of the tested species.     

双膜法处理污水厂尾水效能分析与膜再生研究

为提高污水厂出水水质,寻求适合处理污水厂尾水滤膜的再生方法,采用超滤—纳滤双膜工艺,针对辽宁省本溪市某城市污水厂二级尾水开展深度处理研究。考察了进水流速、累积过滤水量(超滤进水流速为25 L/min,纳滤进水流速为4 L/min)对膜分离效果的影响,同时开展了超滤和纳滤膜再生方式及效果研究。结果表明:在考察范围内,超滤装置的分离性能受进水流速影响较小,主要与进水污染程度有关,对COD、TP、氨氮的平均去除率分别为48%、55%、27%。当纳滤单元进水流速为4 L/min时,双膜法对COD、TP、氨氮的平均去除率分别为87%、96%、68%。双膜法对COD、TP的去除率随着进水污染程度的减轻而降低,氨氮去除率受累积过滤水量的影响较小,这与原水污染程度有关。随着累积过滤水量的增加,膜分离性能呈减弱趋势。超滤膜轻微污染时采用物理清洗效果良好,严重污染时需采用化学清洗的方法。超滤有效延缓了纳滤膜污染,纳滤膜轻微污染时采用酸碱浸泡法再生效果良好。     

Nutrient recovery and crop yield enhancement in irrigation with reclaimed wastewater: a case study

The paper reports results of treated wastewater reuse field experiments carried out in Apulia (Southern Italy). Fennel and lettuce were irrigated with four different water sources: three reclaimed wastewater streams, obtained by applying different treatment schemes to the same municipal wastewater, and a conventional source (well water). Differences between the three effluents were significant in terms of suspended solids and faecal indicators. Both lettuce and fennel yields were enhanced by the high content of nutrients in the effluent of one of the treatment plants, which had been operated for partial nitrogen removal. In particular, fennel productivity was enhanced by replacing chemical fertirrigation with the supply of nutrients contained in the irrigation water.     

A~2/O型膜生物反应器污水处理工艺设计要点

采用旭化成化学株式会社生产的中空纤维膜组件,建立了处理能力为20m3/d的A2/O型膜生物反应器(MBR)系统,对城市污水的深度处理进行了中试研究。试验结果表明系统运行稳定,各项出水指标均达到或优于国家一级A标准。在此基础上,重点介绍了处理规模为30000m3/d,采用A2/O型膜生物反应器系统的总体概念设计。通过计算总结了设计要点,并得出单位经营成本为0.84元/m3,较其他同类工艺成本低。     

The effect of organic loading on process performance and membrane fouling in a submerged membrane bioreactor treating municipal wastewater

The results of experiments on municipal wastewater primary effluent are presented for a pilot-scale submerged membrane bioreactor (SMBR). The SMBR pilot plant employed an ultrafiltration membrane with a nominal pore size of 0.035 microm and was operated at a constant membrane flux of 30 L/m(2)h. The mixed liquor suspended solids (MLSS) concentration was maintained at 8+/-2 g/L and steady-state fouling rates were determined for 10, 5, 4, 3, and 2-d MCRTs, corresponding to food-to-microorganism (F/M) ratios of 0.34, 0.55, 0.73, 0.84, and 1.41 gCOD/gVSS d, respectively. Membrane fouling rates increased as the F/M was increased. Steady-state membrane fouling rates were correlated with total soluble microbial products (SMP) concentrations. The membrane fouling rates did not correlate well with soluble COD measured on a 0.45 microm membrane filtrate of mixed liquor or with soluble COD rejection (effluent COD/soluble COD).     

Reuse of treated municipal wastewater in irrigation: a case study from Lebanon and Jordan

In this study, we present the results of scenarios where secondary‐treated municipal wastewater was used for table grapes irrigation in the region of Ablah, Bekaa valley in Lebanon, and fodder crops irrigation (vetch and barley) in the region of Ramtha in Jordan. In Lebanon, we carried out experiments to assess the response of drip‐irrigated table grapes grown under two water quality regimes (Freshwater (FW) and treated wastewater (TW) and two water levels (100% of evapotranspiration (ETc) and 75% of ETc). While in Jordan, we carried out experiments to assess the response of drip‐irrigated fodder crops considering 4 irrigation levels (Q1: Rain fed; Q2: 80% of ETc; Q3: 100% of ETc; Q4: 120% of ETc) and three crop patterns (C1: Barley 100%; C2: Vetch 100%; C3: Mix 50% barley and 50% vetch). Based on the production and quality components, table grapes were successfully grown on plots that are supplied with TW. Fodder crops were successfully grown using TW with remarkable increase in biomass and grain yield production for the irrigated treatments.     

Viability of a low-pressure nanofilter in treating recycled water for water reuse applications: a pilot-scale study

The purpose of this study was to investigate the potential of a low-pressure nanofiltration (NF) membrane for treating recycled water for indirect potable water reuse applications. In particular, the tradeoffs in choosing low-pressure NF over reverse osmosis (RO) were investigated including whether or not significantly lowering operating pressures/costs would result in diminished permeate water quality. A NF membrane (Dow/Filmtec NF-4040) with high permeate productivity was selected for pilot-scale testing over a period of 1200h at a water reuse facility employing conventional RO membranes for treating tertiary treated wastewater effluent prior to aquifer recharge. The novel application of an NF membrane in treating wastewater effluent for water reuse applications permitted a comprehensive screening of NF permeate water quality and allowed for the investigation of trace organic contaminant rejection on pilot scale with environmentally relevant feed water concentrations. Results from pilot-scale testing highlighted the selectivity of NF membranes in removing organic solutes present in wastewater effluents at the parts-per-trillion level. While operating pressures were by a factor of 2-3 lower than conventional RO membranes, and bulk and trace organic rejection generally exceeded 90 percent, not surprisingly, the rejection of monovalent ions such as nitrate was poor. The poor-to-moderate rejection of monovalent ions, however, resulted in lowered brine stream total dissolved solids concentration and sodium adsorption ratio as compared with the brine stream of conventional RO membranes, which may be beneficial for brine disposal strategies.     

A^2/O+MBR工艺用于集约化高排放标准半地下式污水厂

坂雪岗水质净化厂二期工程位于深圳市龙岗区华为科技城,设计规模为12×10^4 m^3/d。工程用地紧张,出水水质标准高,常规的生物处理工艺很难稳定达标,故生化处理采用A^2/O+MBR膜工艺。全厂污水处理构筑物区域采用半地下式组合式布置,顶部加盖覆土建设市政公园,综合了传统地面式污水厂及全地下式污水厂的优点,环境优美,运行管理方便。生产运行以来,出水水质稳定优于《地表水环境质量标准》(GB 3838-2002)的Ⅳ类标准(总氮≤10 mg/L)。     

Role of hydraulic retention time and granular medium in microbial removal in tertiary treatment reed beds

The main objective of this paper is to evaluate the role of hydraulic retention time (HRT) and granular medium in faecal coliform (FC) and somatic coliphage (SC) removal in tertiary reed beds. Experiments were carried out in a pilot plant with four parallel reed beds (horizontal subsurface flow constructed wetlands), each one containing a different type of granular medium. This pilot plant is located in a wastewater treatment plant in Montcada i Reixac, near Barcelona, in northeastern Spain. The microbial inactivation ratios obtained in the different beds are compared as a function of three selected HRTs. Secondary effluent from the wastewater treatment plant was used as the influent of the pilot system. The microbial inactivation ratio ranged between 0.1 and 2.7 log-units for FC and from 0.5 to 1.7 log-units for SC in beds with coarser granular material (5-25mm), while it ranged between 0.7 and 3.4 log-units for FC and from 0.9 to 2.6 log-units for SC in the bed with finer material (2-13mm). HRT and granular medium are both key factors in microbial removal in the tertiary reed beds. The microbial inactivation ratio rises as the HRT increases until it reaches a saturation value (in general at an HRT of 3 days). The value of the microbial inactivation ratio at the saturation level depends on the granular medium contained in the bed. The specific surface area necessary to reach 2-3 log-units of FC and SC is approximately 3m(2)/person-equivalent.     

啤酒污泥用作城市污水厂种泥的试验研究

为考察啤酒厂污水处理站的脱水污泥（简称啤酒污泥）用作城市污水厂接种污泥的可行性，摸索污泥的培养与驯化规律，采用连续操作、全流量同步培养和驯化方法，在处理能力为500m^2／d的UNITANK池中对啤酒污泥进行了培养和驯化。试验结果表明，啤酒污泥完全可以作为城市污水处理厂的接种污泥使用，而且培养时间短，出水水质好。曝气0．5h、厌氧搅拌1h时，活性污泥增长最快。将DO控制在2mg／L左右有利于活性污泥的增长；当DO长时间在7mg／L以上时，污泥浓度下降趋势明显。污泥浓度达到2000mg／L所需的培养驯化时间仅为5d；使出水水质达到一级B标准所需的培养时间约为6d。这种培养、驯化方法和经验可为其他城市污水处理厂的建设和运行提供参考。     

Impact of colloidal and soluble organic material on membrane performance in membrane bioreactors for municipal wastewater treatment

Two parallel membrane bioreactors (2 m3 each) were operated over a period of 2 years. Both pilots were optimised for nitrification, denitrification, and enhanced biological phosphorous elimination, treating identical municipal wastewater under comparable operating conditions. The only constructional difference between the pilots was the position of the denitrification zone (pre-denitrification in pilot 1 and post-denitrification in pilot 2). Despite identical modules and conditions, the two MBRs showed different permeabilities and fouling rates. The differences were not related to the denitrification scheme. In order to find an explanation for the different membrane performances, a one-year investigation was initiated and the membrane performance as well as the operating regime and characteristics of the activated sludge were closely studied. MLSS concentrations, solid retention time, loading rates, and filtration flux were found not to be responsible for the different performance of the submerged modules. These parameters were kept identical in the two pilot plants. Instead, the non-settable fraction of the sludges (soluble and colloidal material, i.e. polysaccharides, proteins and organic colloids) was found to impact fouling and to cause the difference in membrane performance between the two MBR. This fraction was analysed by spectrophotometric and size exclusion chromatography (SEC) methods. In a second step, the origin of these substances was investigated. The results point to microbiologically produced substances such as extracellular polymeric substances (EPS) or soluble microbial products (SMP).     

Development of biological filter as tertiary treatment for effective nitrogen removal: Biological filter for tertiary treatment

A biological filtration process applicable to tertiary treatment of sewage for effective nitrogen removal was developed. It consisted of a nitrification filter (Filter 1) and/or a polishing filter with anoxic and oxic parts (Filter 2). A pilot plant set at a municipal sewage treatment plant was operated for 525 d with feed of real sewage. The maximum apparent nitrification rate in Filter 1 in winter was 0.54 kg N/m3- filter-bed d. In Filter 2, the maximum denitrification capacity was 4 kg N/m3 filter-bed d) in winter. SS was stably removed and high transparency water was obtained. The target water quality (SS, BOD, and T-N5 mg/L) was accomplished in winter with the LV of 202 m/d in Filter 2, which corresponds to 0.24 h of HRT. These results proved that this process is compact, stable, convenient to install, and cost effective to build and operate as tertiary treatment to remove nitrogen effectively.     

Elimination of enteric bacteria in biological-chemical wastewater treatment and tertiary filtration units

The occurrence and removal of salmonellae and faecal indicators in four conventional municipal wastewater treatment plants (MWTP) were investigated. In addition, we tested the efficiency of a semi-technical scale biological nutrient removal process and three pilot-scale tertiary filtration units in microbial removal. All influent samples collected from MWTPs contained salmonellae from 93 to 11,000 MPN/100 ml and indicator bacteria from about 10(7) to 10(8) CFU/100 ml. The reductions in salmonella numbers achieved in full-scale biological-chemical wastewater treatment and semi-technical scale biological nutrient removal processes were usually between 94% and virtually 100% (99.9%) and indicator bacteria reductions between 2 and 3 log units. Microbial numbers in MWTP effluents could be modelled as a function of effluent residual organic matter, suspended solids and total phosphorus concentrations. Pilot-scale tertiary treatment by rapid sand contact filter, chemical contact filter and biological-chemical contact filter reduced salmonella numbers below the detection limit and faecal coliform numbers on average by 99%, 39% and 71%, respectively. A total of 32 Salmonella serovars were identified among 197 Salmonella isolates from municipal wastewaters. Of the isolates, 32% were resistant to nalidixic acid, indicating reduced sensitivity to ciprofloxacin, the drug of choice in the treatment of salmonellosis. In addition, 18% of the isolates were multiresistant. Our results, especially antibiotic resistant Salmonella strains, indicate that conventional municipal wastewater treatment without efficient tertiary treatment, like filtration or disinfection, may constitute a risk for public health.     

Techno-economic evaluation of soil-aquifer treatment using primary effluent at Ahmedabad, India

A pilot study was carried out in Sabarmati River bed at Ahmedabad, India for renovation of primary treated municipal wastewater through soil aquifer treatment (SAT) system. The infrastructure for the pilot SAT system comprised of two primary settling basins, two infiltration basins and two production wells located in the centre of infiltration basins for pumping out renovated wastewater. The performance data indicated that SAT has a very good potential for removal of organic pollutants, nutrients as well as bacteria and viruses. The SAT system was found to be more efficient and economical than the conventional wastewater treatment systems and hence recommended for adoption. A salient feature of the study is the introduction of biomat concept and its contribution in the overall treatment process.     

Combined coagulation-disk filtration process as a pretreatment of ultrafiltration and reverse osmosis membrane for wastewater reclamation: an autopsy study of a pilot plant

The effects of the combined coagulation-disk filtration (CC-DF) process on the fouling characteristics and behavior caused by interactions between effluent organic matter (EfOM) and the membrane surfaces of the ultrafiltration (UF) and reverse osmosis (RO) membranes in a pilot plant for municipal wastewater reclamation (MWR) were investigated. The feed water from secondary effluents was treated by the CC-DF process used as a pretreatment for the UF membrane to mitigate fouling formation and the permeate from the CC-DF process was further filtered by two UF membrane units in parallel arrangement and fed into four RO modules in a series connection. The CC-DF process was not sufficient to mitigate biofouling but the UF membrane was effective in mitigating biofouling on the RO membrane surfaces. Fouling of the UF and RO membranes was dominated by hydrophilic fractions of EfOM (e.g., polysaccharide-like and protein-like substances) and inorganic scaling (e.g., aluminum, calcium and silica). The desorbed UF membrane foulants included more aluminum species and hydrophobic fractions than the desorbed RO membrane foulants, which was presumably due to the residual coagulants and aluminum-humic substance complexes. The significant change in the surface chemistry of the RO membrane (a decrease in surface charge and an increase in contact angle of the fouled RO membranes) induced by the accumulation of hydrophilic EfOM onto the negatively charged RO membrane surface intensified the fouling formation of the fouled RO membrane by hydrophobic interaction between the humic substances of EfOM with relatively high hydrophobicity and the fouled RO membranes with decreased surface charge and increased contract angle.     

A review of the technological feasibility of aquacultures for municipal wastewater treatment

The technical feasibility of utilising aquacultures for municipal wastewater treatment is reviewed. Aquacultures containing one or more aquatic weeds are cost effective for secondary and tertiary wastewater treatment, compared to the highly energy intensive conventional secondary and tertiary wastewater treatment systems. The major advantages are less capital and maintenance costs required as opposed to conventional wastewater treatment. Aquatic treatment systems utilising one or two aquatic weeds are efficient in substantial removal of phosphorus and nitrogen from the wastewater compared to the conventional secondary and tertiary wastewater treatment systems. Further, biogas generated from the harvested aquatic weed biomass could meet the treatment costs of the aquatic treatment systems utilising these aquatic weeds. Year round treatment of municipal wastewater utilising these aquatic weeds is possible even in the temperate regions of the world by housing the treatment systems in green houses. Other aquatic weeds which have tolerance to extreme cold conditions could be tested to make year round treatment of wastewater in aquatic treatment systems.     

Microbiological aspects of a bioreactor with submerged membranes for aerobic treatment of municipal wastewater

An aerobic membrane bioreactor treating municipal wastewater at complete biomass retention was studied in respect of microbiological parameters over a period of 380 days. The results were compared to those obtained from a conventional activated sludge wastewater treatment plant (WWTP) treating the same wastewater. Microscopically, significant changes in the structure of the flocs and of the ratio between free suspended and aggregated cells could be observed. The presence of filamentous bacteria varied from almost not present to very high numbers. With the exception of short periods after changes in operating conditions, protozoa and metazoa were rarely present in the sludge community. The rate of oxygen consumption and the cell detectability by fluorescence in situ hybridizatio (FISH) with rRNA-targeted oligonucleotide probes were used to assess the physiological state of the bacterial cells Oxygen consumption rates of sludge samples obtained from both the conventional and membrane filtration plant wer determined without and after addition of different energy and carbon sources. In contrast to the conventional activate sludge, a pronounced increase in respiration activity upon the addition of organic substrates could be observed in th membrane filtration sludge. In situ probing with the Bacteria-specific probe EUB338 visualized 40-50% of all DAPI stainable bacteria in the membrane bioreactor, compared to 80% cells detectable by FISH in the conventional activate sludge. These results suggest that bacteria present in the highly concentrated biomass of the membrane reactor use the energy supplied for their maintenance metabolism and were not in a physiological state characteristic for growth This assumption could explain the zero net biomass production observed in the reactor.     

Identification of wastewater sludge characteristics to predict critical flux for membrane bioreactor processes

The effects of sludge characteristics on critical flux were examined using a submerged membrane bioreactor pilot plant operated under different process conditions to treat municipal wastewater. The sludge in the membrane tank was characterized by measuring colloidal particle concentration, extracellular polymeric substances (EPS), mixed liquor suspended solids (MLSS), temperature, time to filter (TTF) and diluted sludge volume index (DSVI). The colloidal particle concentration was represented by the colloidal total organic carbon (TOC), which is the TOC difference between the filtrate passing through a 1.5 microm pore size filter and the permeate collected from pilot ultrafiltration membrane modules with a pore size of 0.04 microm. The results showed that the critical flux measured by the stepwise flux method was almost solely related to the colloidal TOC despite different sludges tested. In contrast, MLSS was shown to have little impact on the critical flux within the range examined. Neither TTF nor DSVI could be used to reliably predict the critical flux. Furthermore, colloidal TOC can be attributed to soluble EPS, but not bound EPS. Therefore, it is suggested that colloidal TOC be used as a new filterability index for MBR processes in wastewater treatment.     

污水再生利用水质标准和处理工艺探讨

城镇污水处理厂处理出水具有水量、水质稳定可靠的特点,对其进行再生回用可以减少污染物的排放,缓解水资源紧缺.简述了我国污水再生利用的现状,从农田灌溉、城市杂用、工业用水、环境用水和地下水回灌等五方面介绍了我国城市污水再生利用的相关标准,分析了再生水处理的各种技术,并提出了实施污水再生利用的措施和建议.     

Life cycle assessment of a coupled solar photocatalytic-biological process for wastewater treatment

A comparative life cycle assessment (LCA) of two solar-driven advanced oxidation processes, namely heterogeneous semiconductor photocatalysis and homogeneous photo-Fenton, both coupled to biological treatment, is carried out in order to identify the environmentally preferable alternative to treat industrial wastewaters containing non-biodegradable priority hazardous substances. The study is based on solar pilot plant tests using alpha-methyl-phenylglycine as a target substance. The LCA study is based on the experimental results obtained, along with data from an industrial-scale plant. The system under study includes production of the plant infrastructure, chemicals, electricity, transport of all these materials to the plant site, management of the spent catalyst by transport and landfilling, as well as treatment of the biodegradable effluent obtained in a conventional municipal wastewater treatment plant, and excess sludge treatment by incineration. Nine environmental impact categories are included in the LCA: global warming, ozone depletion, human toxicity, freshwater aquatic toxicity, photochemical ozone formation, acidification, eutrophication, energy consumption, and land use. The experimental results obtained in the pilot plant show that solar photo-Fenton is able to obtain a biodegradable effluent much faster than solar heterogeneous photocatalysis, implying that the latter would require a much larger solar collector area in an industrial application. The results of the LCA show that, an industrial wastewater treatment plant based on heterogeneous photocatalysis involves a higher environmental impact than the photo-Fenton alternative, which displays impact scores 80-90% lower in most impact categories assessed. These results are mainly due to the larger size of the solar collector field needed by the plant.