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This study benchmarks vermifiltration (VF) as secondary wastewater treatment in three nature-based decentralized treatment plants using life-cycle assessment. The comparison is justified by the comparatively easier and cheaper operation of VF when compared to more traditional technologies, including small rate infiltration (SRI), constructed wetlands (CW), and activated sludge (AS). Standard life cycle assessment was used and applied to three case studies located in southern Europe. Material intensity during construction was highest for VF, but impacts during operation were lower, compensating those of the other phases. Impacts during the construction phase far outweigh those of operation and dismantling for facilities using constructed wetlands and activated sludge, when the number of served inhabitants is small, and due to lack of economies of scale. VF used as secondary treatment was shown to contribute to reducing the environmental impacts, mainly in constructed wetlands and activated sludge. The replacement of CW by VF seems to bring important environmental benefits in most impact categories, in particular in the construction phase. The replacement by VF in facilities with SRI seems to result in the improvement of some of the impact categories, in particular in the operation phase. As for dismantling, no conclusive results were obtained. HIGHLIGHTS Vermifiltration is a promising technology.; An LCIA is needed to better understand vermifiltration.; The quantification of the environmental impacts will help researchers in future works.; Constrution, operation and dismantling phases are crucial to understand the life cycle in Wastewater Treatment Plants.; LCIA is an important tool to study the environmental impacts of wastewater treatment.

Most cold-climate biological nutrient removal facilities experience poor settling mixed liquor during winter, resulting in treatment capacity throughput limitations. The Metro Wastewater Reclamation District in Denver, Colorado, operated two full-scale secondary treatment trains to compare the existing biological nutrient removal configuration (Control) to one that was modified to operate with an anaerobic selector and with hydrocyclone selective wasting (Test) to induce granulation. Results from this evaluation showed that the Test achieved significantly better settling behaviour than the Control. The difference in the mean diluted SVI30 between the Test and Control were statistically significant (P < 0.05), with values of 77 ± 17 and 135 ± 25 mL/g observed for the Test and Control respectively. These settling results were accompanied by differences in the particle size distribution, with notably higher settling velocities commensurate with increasing particle size. The degree of granulation observed in the Test train was between 32 and 56% of the mass greater than ≥250 μm in particle size whereas 16% of the mixed liquor in the Control was ≥250 μm over the entire study period. The improved settling behaviour of the Test configuration may translate into an increase of secondary treatment capacity during winter by 32%. HIGHLIGHTS Inducing granulation in a full-scale continuous flow activated sludge system was possible with the application of both biological and physical selection pressures.; Observations in this study could translate to a cost effective intensification solution versus traditional expansion for WRRFs evaluating capacity needs.

This study investigated the impact of each treatment stage of the activated sludge process on the fate of antibiotic resistant bacteria (ARB) in wastewater treatment plants (WWTPs). Wastewater and sludge samples were collected monthly at each stage of a commercial-scale WWTP. After 20–25 strains of indicator Escherichia coli were isolated from each sample on Chromocult Coliform Agar, antibiotic resistance of the isolates to amoxicillin (AMX), ciprofloxacin (CIP), norfloxacin (NFX), kanamycin (KM), sulfamethoxazole/trimethoprim (ST) and tetracycline (TC) were tested with the Kirby–Bauer disk diffusion method. As a result, activated sludge in the aeration tank and return sludge had higher abundance of antibiotic resistant E. coli than influent wastewater and secondary treatment effluent. AMX resistant E. coli was enriched in return sludge at the secondary clarifier. Higher temperature was also likely to cause an increase of AMX resistant E. coli in sludge. The antibiotic resistance profile of E. coli in secondary treatment effluent was more dependent on activated sludge than influent wastewater. These results suggested that activated sludge in WWTP possibly serves as a reservoir of ARB, and that behavior of ARB in WWTP differs by antibiotic classes.

Settling of activated sludge particles has long been the key to successfully achieving secondary treatment. While soluble products can be converted to particulate components via microbial reactions in the activated sludge process, it is the subsequent removal of these particulate components that is the key to achieving ultimate water quality criteria. An understanding of the operating parameters for selecting good settling activated sludge particles was first documented in the 1970s and 1980s. An understanding of the growth pressures that can be imposed on filamentous organisms, and the impacts of selector zones in general, allowed the design and operation of activated sludge processes to routinely achieve good sludge settleability. More recently, research has identified what could be the next evolution in flocculant growth, with the growing interest in aerobic granular sludge. Aerobic granular sludge is purported to provide superior settling properties, and many of the growth pressures identified for aerobic granular sludge are also present in activated sludge systems. These enhanced settling sludge systems are gaining significant interest, but the factors leading to enhanced sludge settleability could be present in historical and existing systems. Three facilities were evaluated that exhibited enhanced settleability (i.e. sludge volume indices of less than 70 mL/g the majority of the time) to determine how these enhanced settling sludges compare to typical settling curves from the literature. The enhanced settling sludge facilities exhibit key differences related to surface overflow rate, return activated sludge (RAS) pumping requirements, and sensitivity to solids concentration that are critical for developing effective settling designs for enhanced settling sludge facilities. As more facilities aim to achieve enhanced settling sludge for intensification of infrastructure, it will be important to carefully consider historic settling curves and to develop site-specific settling criteria when possible.

Fats, Oils, and Grease (FOG) wastes and high-strength wastes (HSW) are frequently received at municipal water resource recovery facilities (WRRFs) as trucked-in wastes. These wastes offer significant benefits in terms of revenue from tipping fees and feedstock for co-digestion in anaerobic digesters that produce biogas, which can be beneficially used as fuel. The number of treatment plants receiving and beneficially using trucked-in wastes currently in operation or under investigation is increasing rapidly across the North America as utilities strive to remove this material from normal wastewater to avoid sewer system clogging, maintenance and backups, avoid the oxygen demand of these wastes in secondary treatment systems, and to capture and beneficially reuse the energy that is contained within the material. Historically, trucked-in wastes have been discharged to the head end of treatment plants or to an upstream manhole in the incoming interceptor sewer to enable the material to be mixed with raw wastewater prior to treatment through the liquid stream of the WRRF. However, this approach results in loss of material and degradation of the energy value of the FOG wastes and HSW and also creates collection and maintenance issues in the preliminary and primary treatment systems. To prevent degradation of the material and retain maximum energy for the CHP system, receiving stations are being constructed for direct off-loading of the wastes to processing and storage facilities prior to their transfer to anaerobic digesters at a relatively uniform rate to minimize the potential for digester upsets while at the same time to increase biogas production. This paper presents the key components and considerations in the design and operation of modern FOG waste receiving and processing facilities.

Wastewater management in Greece is being regulated by the Urban Waste Water Treatment Directive (UWWTD) and as a result many wastewater treatment plants (WWTPs) have been constructed during the last 30 years and are in operation. The present work aims to outline the progress regarding the implementation of the specific environmental policy, present deficiencies and future challenges, while an evaluation of the performance is conducted for small-medium and large WWTPs focusing on the influent and effluent quality characteristics. In Greece the existing level of treatment provided is related to secondary treatment for the removal of organic load, which in most cases is supplemented by nitrogen removal (for more than 85% of the WWTPs) and phosphorus removal. With respect to the characteristics of the raw municipal wastewater these correspond to typical low to medium strength sewage. Compliance to the UWWTD effluent standards for BOD5, COD and SS is achieved in more than 90% of the WWTPs, while in terms of nutrients, 80% of the WWTPs efficiently remove nitrogen and approximately 45% of the WWTPs remove phosphorus.

Constructed wetlands (CWs) represent low-cost technology for the treatment and reuse of wastewater in urban areas. This study aimed to evaluate the pollutant removal efficiency of a CW system and to assess the effects of irrigation using treated urban wastewater on soil and on two warm-season turf species. The research was carried out in Sicily (Italy) on a pilot-scale horizontal subsurface flow system which was fed with treated urban wastewater following secondary treatment from an activated-sludge wastewater treatment plant. The pilot system was located in an open urban park and comprised two separate parallel planted units. Experimental fields of Cynodon dactylon (L.) Pers. and Paspalum vaginatum Sw. were set up close to the system and irrigated with both treated wastewater (TWW) and freshwater (FW). Irrigation with TWW did not result in a significant variation in soil pH and soil salinity in the topsoil. The turf species tolerated high sodium levels in the soil due to TWW irrigation. Savings in FW and mineral fertilizers were deemed significant. The results highlight the fact that use of CW systems for the treatment and reuse of wastewater can represent a sustainable way to obtain alternative water resources for turfgrass irrigation in urban areas.

A two-stage vertical flow treatment wetlands system (French reed beds) was realized in 2012–2013 for the Orhei's town in Moldova. The treatment system occupies a total area of about 5 ha and operates in cold climate conditions during winter, with air temperatures below −20 °C. The first 2 years (2013–2015) of treatment performances for this system are presented here, with a particular highlight on the analysis of the commissioning phase and the operative choices taken along this period basing on the observed results. The specific classification of this application of constructed wetlands (CWs) for the primary and secondary treatment of municipal wastewater as a medium-large size system makes this technical report a relevant reference for demonstrating the possible extension to the highest numbers of inhabitants for the common application range of this family of technologies (CWs) for municipal wastewater. The observed performances for organic carbon (both as chemical oxygen demand (COD) and biochemical oxygen demand (BOD5)), suspended solids and ammonia removals in the whole first operational period consistently satisfied the national limits for discharge in rivers, respectively, with average values of 86%, 96% and 66%. The treated daily flow was measured in the range of 1,000–2,000 m3/d.

A sustainable membrane operation often requires pretreatment of the feed liquor to improve its technical and economic feasibility. This paper reports the impact of pretreatment on the performance of ceramic microfiltration for several pilot studies at different locations. Four different pretreatment processes were investigated: (1) in-line coagulation (to remove high molecular weight, HMW, dissolved organic carbon, DOC); (2) ion exchange (to remove low molecular weight, LMW, DOC); (3) ozone (for disinfection, taste and odor control, and modifying the character of DOC) (4) ion exchange followed by in-line coagulation (for almost complete removal of DOC). Pretreatment in all cases was needed to control membrane fouling, to establish a technically and economically feasible process. These studies seem to show that the DOC's HMW (which includes biopolymers) and LMW fractions (the latter includes humics/acids), are primarily responsible for the TMP increase after filtration followed by backwashing (irreversible fouling). Removing one of these organic fractions often results in more stable operation. Ozonation in all cases led to better operation, but is not always economically feasible. The feasibility of ozone as pre-treatment depends largely on the initial ozone demand, and whether or not there are secondary treatment targets (e.g., higher virus removal, taste, and/or odor).

Five municipal and domestic wastewater treatment plants, most of which had secondary treatment systems formed by activated sludge, were studied during 2013–2014 in Tehran. The study was done in order to evaluate their efficiency in terms of removal of Cryptosporidium and Giardia by (oo)cyst recovery in effluent samples using immunofluorescence with monoclonal antibodies. Results showed that mean concentrations of cysts in the influent samples always outnumbered mean concentrations of oocysts (883.3 ± 4,16.7–3,191.7 ± 1,067.2 versus 4.8 ± 6.2–83.8 ± 77.3 (oo)cysts/L), and that lower concentrations of (oo)cysts were recorded in summer, and higher levels in autumn, and that the difference was statistically significant (t-test, P 0.05). Infections in mice inoculated with cysts obtained from urban wastewater effluent demonstrated presence of infectious Giardia cysts. Results demonstrate limited efficiency of conventional wastewater treatment processes at physico-chemical removal of (oo)cysts.

The presence of organic compounds in water sources is one of the concerns in water treatment. They are potential precursors of disinfection byproducts (DBPs) and thus induce health problems in humans. Among the emerging DBPs, carcinogenic compound N-nitrosodimethylamine (NDMA) has been receiving attention during the last decade. This study examined the characteristics of organic components in various water sources and investigated their relationships with NDMA formation. Experiments were carried out on selected water samples from both natural water and wastewater. Results showed similar NDMA formation kinetics for both water sources. However, more contribution of NDMA precursors was found to be from the wastewater due to its higher organic nitrogen content. NDMA formation potential (NDMAFP) of secondary effluent ranged from 264 to 530 ng/L. A correlation study between organic compound characteristics and NDMAFP indicated that the majority of NDMA precursors came from dissolved organic nitrogen (DON) compound with small molecular weight (smaller than 500 Da), with correlation R2 = 0.898. Although secondary treatment removed more than 90% of NDMA precursors, the remaining precursors in secondary effluent would still pose a challenge for water quality.

Conventional membrane bioreactor (MBR) systems have increasingly been studied in recent decades. However, their applications have been limited due to their drawbacks such as low flux, membrane fouling, and high operating cost. In this study, a compact macro-filtration MBR (MfMBR) process was developed by using a large pore size membrane to mitigate the membrane fouling problem. A pilot trial of MfMBR process was set up and operated to treat 10 m3/day of saline wastewater within 4 h. The system was operated under an average permeate flux of 13.1 m3/(m2·day) for 74 days. The average total suspended solids, total chemical oxygen demand, biological oxygen demand, total Kjeldahl nitrogen, and total nitrogen removal efficiencies achieved were 94.3, 83.1, 98.0, 93.1, and 63.3%, respectively, during steady-state operation. The confocal laser scanning microscopy image indicated that the backwash could effectively remove the bio-cake and dead bacteria. Thus, the results showed that the MfMBR process, which is essentially a primary wastewater treatment process, had the potential to yield the same high quality effluent standards as the secondary treatment process; thereby suggesting that it could be used as an option when the economic budget and/or land space is limited.

A wastewater biofiltration model is used to assess the potential of modelling plant-sized secondary carbon removal biofilter units. Two distinct datasets collected at the Seine-Centre biofiltration plant (Colombes, France) are used. The model is first calibrated on multiple grab samples taken at different heights inside the filter media. Data from 24 hour composite samples at the unit influent and effluent over a 2 year period are then simulated. Additional data are used to estimate hourly concentration profiles from composite samples in order to correctly use both composite and grab samples during modelling. The calibrated model is in most cases able to correctly predict the general nutrient behaviour for both datasets. The results of statistical scores such as the mean error and the mean absolute error are low for soluble components and remain correct for particles during years 2008–2009. Only one parameter set containing few heavily modified values is used to obtain these results. Modelling plant-sized biofilters appears to be practical and can be useful for easily evaluating plant optimization scenarios.

Activated sludge flocs that are carried to the final effluent can significantly decrease the effectiveness of ultraviolet (UV) disinfection of wastewater. This effect is detected in a typical UV dose–response curve, where at higher UV doses there is a decrease in the inactivation rate (tailing). In this study, the effect of activated sludge process conditions on the UV inactivation kinetics of flocs was investigated. The conditions compared were nitrifying vs. non-nitrifying vs. an enhanced biological nutrient removal–University of Cape Town (BNR-UCT) system. The results showed that the flocs generated in the BNR-UCT process were easier to disinfect. The final effluent from the BNR-UCT process also showed improved kinetics of inactivation and reached higher levels of disinfection. The nitrifying system's final effluent had a lower number of initial fecal coliforms, which contributed to reaching higher disinfection levels compared to the non-nitrifying system.

Increased incidence of antibiotics in human-affected environments is raising concerns about increase in acquired antibiotic resistance by environmental bacteria. Wastewater collection and treatment systems are likely significant anthropogenic sinks and vectors for antibiotics and associated antibiotic resistance. Typical municipal treatment plants collect wastewaters of various sources, including well-established antibiotic resistance reservoirs such as hospitals, intensive care units and nursing homes, and integrate them with sources not commonly identified as major sources of antibiotic resistance, such as residential or industrial sources. A comprehensive PCR-DGGE diversity analysis of wastewater antibiotic-resistant bacteria was performed to evaluate the role of various wastewater sources in the discharge of antibiotic resistance by a municipal treatment plant. Wastewater sources are clearly inducing resistance in the final effluent but the role of each source type is highly variable, likely as a function of variable environmental conditions or water use patterns. Comparisons between primary treatment and secondary treatment stages indicate a strong role of the intensity of the wastewater treatment in the diversity profiles of antibiotic-resistant bacteria. While pervasiveness of antibiotic resistance in the system impedes clear discrimination between sources in the tested system, there are indications of specific source type related impacts.

The Arlington County Wastewater Pollution Control Plant (ACWPCP) is located in the southern part of Arlington County, Virginia, USA and discharges to the Potomac River via the Four Mile Run. The ACWPCP was originally constructed in 1937. In 2001, Arlington County, Virginia (USA) committed to expanding their 113,500 m3/d, (300,000 pe) secondary treatment plant to a 151,400 m3/d (400,000 pe) to achieve effluent total nitrogen (TN) to

Two wastewater polishing systems were compared in terms of their ability to protect downstream reverse osmosis (RO) processes. A conventional full-scale wastewater treatment system with primary and secondary treatment followed by rotating biological contactors (RBC) and sand filtration were compared in a side-by-side study with a pilot-scale membrane bioreactor (MBR). Effluent from the two pretreatment trains was sent to two identical RO pilot systems. The effluent water quality of the two systems was compared as well as the RO performance. The MBR pretreatment provided effluent with a turbidity (0.11 NTU) that was more than five times lower than that of the conventional system (0.58 NTU). The fouling rate of the RO system with MBR pretreatment was 50–67% of the value found for the RO system with conventional pretreatment and the difference in turbidity values was identified as the major source of this large difference. The RO effluent quality of both systems was excellent, with similar overall removals in both systems. The study emphasizes the importance of removing particulate matter for the prevention of RO fouling within water reclamation.

Concerns about water shortage and pollution have received increased attention over the past few years, especially in developing countries with warm climate. In order to help local water management in these countries, the Euro-Mediterranean Regional Programme (MEDA) has financed the Zer0-m project (E-mail: www.zer0-m.org). As a part of this project, several constructed wetland (CW) pilot systems with different pre-treatments have been implemented in four Technological Demonstration Centres in Egypt, Morocco, Tunisia and Turkey. The aim of this research was to establish appropriate designs for treatment of segregated domestic black (BW) and grey water (GW). We tested several different multistage CW configurations, consisting of horizontal and vertical subsurface flow CW for secondary treatment and free water systems as tertiary stage. CW removal efficiencies of TSS, COD, BOD(5), N-NH(4)(+), N-NO(3)(-), N(tot), total coliforms (TC) were evaluated for each of the implemented systems. The results from this study demonstrate the potential of CWs as a suitable technology for treating segregated domestic wastewater. A very efficient COD reduction (up to 98%) and nitrification (92-99%) was achieved for BW and GW in all systems. CW effluent concentrations were below 15 mg/L for BOD(5), 1 mg/L for N-NO(3)(-) and 0.5 mg/L for N-NH(4)(+) together with acceptable TC counts. Based on these results, we suggest adopting the design parameters used in this study for the treatment of segregated wastewater in the Mediterranean area.

With Chemically Enhanced Primary Treatment (CEPT) as the short-term process, the capacity of Bailonggang Wastewater Treatment Plant accounts for almost 25% of the total capacity of wastewater treatment in Shanghai, China. However, shortly after this plant was placed in operation in 2004, it was found that the effluent of CEPT couldn't meet the new national discharge criteria. Although the removal of phosphate is almost 80%, chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) in the effluent is frequently found to exceed the standards. The primary goal of this research is to investigate the possibility of optimizing the CEPT to make it meet the discharge criteria before it is upgraded to a secondary treatment. An oxidant is adopted to remove NH3-N, and a high performance polyaluminum chloride (HP-PACl) is synthesized to enhance the removal of COD. It is found that HP-PACl improves the removal of COD, and the oxidant enhances NH3-N removal effectively. However, to meet the requirement of a newly implemented stricter discharge standard, it is necessary to upgrade this CEPT to a secondary treatment. The results of this study provide scientific evidence for the upgrade of the Bailonggang Wastewater Treatment Plant.

The pathogen loads within surface waters originating from urban wastewater sources needs to be assessed to support drinking water risk estimations and optimal selection of risk reduction measures. Locally reported discharges from sewer systems (>100,000 persons connected) were used to simulate the potential microbial loads into the Göta älv river, Sweden. Using Monte Carlo simulations, the median and 95% percentile (i.e. worst case) of total microbial load from wastewater treatment plants, sewer network overflows and emergency discharges were assessed and presented for dry and wet weather conditions. Wastewater treatment plants with secondary treatment represented a major source of E. coli, norovirus, Giardia and Cryptosporidium. During wet weather, comparably high microbial loads were found for sewer overflows due to heavy rains. Substantial loads were also associated with an incident of the emergency discharge of untreated wastewater. Simulated river water concentrations of faecal indicators (E. coli, sulfite reducing clostridia, somatic coliphages) and pathogens (norovirus, Giardia, Cryptosporidium) were confirmed by river sampling data, suggesting that urban wastewater is the major microbial source for this river.

A wastewater treatment plant consists of unit processes designed to achieve specific waste reduction goals. Offensive odors associated with these treatment processes are a constant source of public complaints. The purpose of this study was to statistically determine the process parameters that influence the formation of volatile sulfur compounds (VSCs) in the secondary treatment system. A statistical model was developed to relate the process parameters to the formation of VSCs in this system. The model established that F/M ratio, sludge blanket depth and SSV60 were the dominant process parameters that influenced the formation of VSCs in the secondary sedimentation basin. This model provides a useful tool for plant engineers to predict and control the VSC formation in a secondary activated sludge treatment system.

The present paper describes the development of Sulphidogenesis Cum Ammonia Removal Process (SCARP) with a simple sulphide inhibition control. The process was developed using synthetic effluent and its application for treatment of primary treated tannery effluent was demonstrated. This paper also discusses the effects of HRT and loading rates. The developed SCARP could treat efficiently the primary treated tannery effluent with influent concentrations of COD, SO42− and NH4+ equal to 3,900 mg/L, 3,000 mg/L and 300 mg/L, respectively. An HRT of 10.5 hours was found to be adequate for COD, NH4-N and SO42− loading rates of 8.9 kg COD/m3/d, 0.68 kg NH4+/m3/d, 6.84 kg SO42−/m3/d, respectively. The overall removal efficiencies of COD, NH4-N and SO42− for the above loading rates were in the ranges of 90.8–91.8%, 84–88.3% and 64.2–70.2%, respectively. The system performance was satisfactory for different loading rates and low COD/SO42− ratios. The developed SCARP has good potential as a cost effective alternative treatment process to existing extended aeration process with nitrification–denitrification for the secondary treatment of tannery effluent.

Samples collected every two weeks from the inlet and outlet of three sewage treatment plants were screened for the presence of noro-, rota-, astro-, adeno-, hepatitis A- and circoviruses by (RT)-nested PCR, and for F-specific bacteriophages by isolation in Escherichia coli Famp. Plants A and B were secondary treatment plants and plant C used primary treatment. Noroviruses were detected in 43%, 53% and 24% of the inlet samples and 26%, 40% and 21% of the outlet samples from plants A, B and C, respectively. Astroviruses, rotaviruses and adenoviruses were more prevalent. Adenoviruses were detected in 96% of inlet and 94% of outlet samples, supporting the potential of these viruses as indicators of viral contamination from sewage. Hepatitis A virus and circoviruses were found only rarely. Reduction of infective viral particles during sewage treatment was evaluated using F-specific bacteriophages. The phages were reduced by, respectively, 99%, 87% and 0% in plants A, B and C, which corresponded to the observed differences in reduction of norovirus positive samples between the same plants. The study shows that the high viral load in sewage results in a discharge to the environment of a large amount of virus despite sewage treatment. On the other hand, the advantage of a more advanced treatment is demonstrated.

This paper describes the moving bed biofilm reactor (MBBR) and presents applications of wastewater treatment processes in which this reactor is used. The MBBR processes have been extensively used for BOD/COD-removal, as well as for nitrification and denitrification in municipal and industrial wastewater treatment. This paper focuses on the municipal applications. The most frequent process combinations are presented and discussed. Basic design data obtained through research, as well as data from practical operation of various plants, are presented. It is demonstrated that the MBBR may be used in an extremely compact high-rate process (

The STP Uithoorn will be upgraded to accommodate the treatment of wastewater from a growing population and to meet more stringent nutrient discharge limits in 2006. In 2003 a system choice and preliminary design was made for the upgrading. A special feature is the nutrient rich wastewater flow from the rapidly developing horticulture in the area. Since the future loads from horticulture are highly uncertain, flexibility of the STP after upgrading is an important issue. A three stage system was selected: improved physical-chemical primary treatment, secondary treatment by activated sludge, and tertiary treatment by denitrifying filters. In this way an important part of the existing infrastructure can be reused, and flexibility is assured by constructing the tertiary treatment in modules and by providing a wide range of operational control possibilities. In this paper the process of system choice and selection of type of tertiary treatment are described, as well as the optimisation of the existing treatment. In order to determine the feasibility of allowing a high loading rate on the existing secondary clarifiers, a two-dimensional hydraulic model of the clarification process was used.

Two high-rate, anaerobic/aerobic units were used to treat the sewage of the Institut Agronomique st Vétérinaire Hassan II (Morocco) campus in a 1,100 m2-plant designed for 1,500 e.p. and receiving 63 m3 per day. The anaerobic pre-treatment consisted of a two-step up-flow anaerobic reactor (TSUAR) comprising two reactors and one external settler all in series. The aerobic line, or post-treatment, consisted of a high-rate algal pond (HRAP) and one maturation pond in series. The system totalized a hydraulic retention time (HRT) of 9 days. A gravel filter (GF) was constructed behind the TSUAR to trap low-density particles. The TSUAR removed 80% of COD and 90% of SS within 48 h. Solids retention time in the reactors averaged 32 d with a specific sludge production of 0.28 g SS g−1 COD removed. Almost 93% of the sludge evacuated from the settler was stabilized. Specific biogas production from both reactors was 0.25 m3 kg−1 COD removed. Used in this configuration, the HRAP lost its BOD removal activity and increased its nutrients and pathogens removal capabilities (tertiary treatment). Results showed that 85% of total nitrogen and 48% of total phosphorus were removed by the HRAP. Land area requirement of this combination was less than 1 m2 per capita and filtered final effluent was of excellent quality (COD, 82 mg/l; TKN, 8.3 mg/l; total P, 2.7 mg/l, faecal coliforms, 2.4 103/100 ml and zero helminths eggs).

Bolivar Wastewater Treatment Plant (WWTP) was originally commissioned with trickling filter secondary treatment, followed by waste stabilisation pond (WSP) treatment and marine discharge. In 1999, a dissolved air flotation/filtration (DAFF) plant was commissioned to treat a portion of the WSP effluent for horticultural reuse. In 2001, the trickling filters were replaced with activated sludge treatment. A shift in WSP ecology became evident soon after this time, characterised by a statistically significant reduction in algal counts in the pond effluent, and increased variability in algal counts and occasional population crashes in the ponds. While the photosynthetic capacity of the WSPs has been reduced, the concomitant reduction in organic loading has meant that the WSPs have not become overloaded. As a result of the improvement in water quality leaving the ponds, significant cost savings and improved product water quality have been realised in the subsequent DAFF treatment stage. A number of operating issues have arisen from the change, however, including the re-emergence of a midge fly nuisance at the site. Control of midge flies using chemical spraying has negated the cost savings realised in the DAFF treatment stage. While biomanipulation of the WSP may provide a less aggressive method of midge control, this case demonstrates the difficulty of predicting in advance all ramifications of a retrospective process change.

Reed beds (horizontal subsurface flow constructed wetlands) have been employed as secondary treatment devices in on-site and decentralised wastewater management systems in the northeast of the Australian state of New South Wales (NSW) for over a decade. This paper summarises some of the practical and research findings that have come to light in that time. Experience with various aspects of reed bed structure is discussed. A study of the evaporative performance of four small beds planted with Phragmites australis yielded an annual crop factor of 2.6. A total of 28 studies on reed beds treating a variety of commonly encountered wastewater streams yielded the following mean pollutant removal efficiencies: total suspended solids (TSS) 83%, biochemical oxygen demand (BOD) 81%, total nitrogen (TN) 57%, total phosphorus (TP) 35% and faecal coliforms (FC) 1.9 logs. The reed bed is becoming the preferred on-site technology for removing TN and BOD and polishing TSS from primary settled domestic wastewater. Sizing beds for a residence time of approximately five days has become standard practice. A study of six reed beds found six different species of earthworm present, mainly Perionyx excavatus (Indian Blue). A mesocosm experiment subsequently showed that the worms were translocating clogging material from the substrate interstices to the surface of the bed thereby indicating a possible method for prolonging reed bed life.

Designers of on-site wastewater management systems have six opportunities to remove pollutants of concern from the aqueous waste stream before it reaches ground or surface waters. These opportunities occur at source, at point of collection (primary treatment), secondary treatment, tertiary treatment, land application and buffers. This paper presents a computer based model for the sizing of on-site system land application areas applicable to the Lismore area in Northern New South Wales, a region of high rainfall. Inputs to the model include daily climatic data, soil type, number of people loading the system and size of housing allotment. Constraints include allowable phosphorus export, nitrogen export and hydraulic percolation. In the Lismore area nitrogen is the nutrient of most concern. In areas close to environmentally sensitive waterways, and in dense developments, the allowable annual nitrogen export becomes the main factor determining the land application area size. The model offers system designers the opportunity to test various combinations of nitrogen attenuation strategies (source control, secondary treatment) in order to create a solution which offers an acceptable nitrogen export rate while meeting the client's household and financial needs. The model runs on an Excel spreadsheet and has been developed by Lismore City Council.

Reuse of wastewater effluents from secondary treatment processes in municipal wastewater treatment plants has been issued because of substantial volumes of relatively clean waters. The major components of criteria for wastewater reclamations are color, organic matter, and pathogens. An advanced oxidation process with low-pressure ultraviolet and hydrogen peroxide addition (UV/H2O2 system) has been employed for removal of the major components in the criteria for reuse of wastewater. Sand filter pretreatment was applied to remove turbidity and to improve performance of UV irradiation. The results showed that total coliforms were effectively inactivated by the UV irradiation alone with the contact time of 30 minutes but color was remained. The addition of H2O2 significantly improved the removal of color and dissolved organic matter in the same contact time.

In 2003 the Aquarec project sponsored by the European Commission under the 5th Framework Programme was started, aiming at “integrated concepts for reuse of upgraded wastewater with special focus on the European countries”. One of the key elements is the development of a treatment matrix, in which wastewater treatment processes are categorised as a function of the raw wastewater quality and the reuse application and are further characterised with respect to costs, operational critical control points and environmental aspects. The construction of the treatment matrix is based on the reuse options (industrial, domestic, natural and agricultural applications), the water quality requirements, the treatment requirements and the extensive description of the various treatment processes and schemes. In the process of constructing the matrix it can be concluded that the actual knowledge on municipal wastewater treatment is definitely well consolidated until the so-called secondary treatment including biological or physical/chemical nutrients removal; the treatment of this effluent should be accomplished by more advanced techniques. As a consequence of the actual EU rules on water discharges, it makes sense to focus the Aquarec project on the possible refinements of secondary effluent. Great attention must be given to the advanced or tertiary wastewater treatment processes, as a mean to upgrade the effluent to water suitable for reuse.

Within the context of this study, two lab-scale aquatic plant reactors consisting of duckweed (Lemna minor) ponds, were investigated for the removal of nitrogen forms during the secondary treatment of domestic wastewater. TKN, NH3-N and NO3-N parameters have been measured in both reactors for hydraulic retention times ranging from 3.3 days to 23 days and at various distances from the inlet of reactors. The results were evaluated for hydraulic retention times, hydraulic loading rates and mass loading rates. It was concluded that hydraulic and mass loading parameters were more meaningful than hydraulic retention time. Optimum nitrogen removal values of hydraulic loading rate and mass loading rate were found to be 1.2 cm/day and 90-160 mg TKN/m2-day, respectively. At the higher and lower loading rates, nitrogen removal efficiency was lower than those at optimum conditions. Effluent TKN concentration was around 2.5 to 3.0 mg/l while NH3-N concentration was almost zero at these loading conditions. On the other hand, effluent NO3-N concentrations changed between 7 mg/l to 11 mg/l. When investigating the longitudinal profile, values were reduced rapidly along the reactors. It was concluded that most of the nitrogen conversion occurred at the beginning of the reactor.

Yannawa Wastewater Treatment plant (Phase 1) serves a population equivalent of 500,000 and is located on a restricted site within the city of Bangkok, Thailand. Secondary treatment is based on the CASS sequencing batch reactor (SBR) process and the plant is one of the largest multi-storey SBRs in the world. The limitation of available site area, the ground conditions and the characteristics of the wastewater to be treated set a series of challenges for the designers, contractors and commissioning and operational staff. This paper briefly describes the collection system, the process selection and the treatment streams of the wastewater treatment plant. The SBR secondary treatment plant is described in more detail. The problems that arose during commissioning and operation and the solutions made possible by the use of an SBR type of process are discussed. Details of plant performance during performance testing and during the first three years of plant operation are provided.

Cost-effective solutions are a must in developing countries, not only regarding investment costs, but also in respect to technology and operating practices. With these two goals in mind, in Brazil a particular effort has been directed for the development and application of the Chemical Enhanced Primary Treatment (CEPT) process and of the Upflow Anaerobic Sludge Blanket (UASB) process, both followed by complementary secondary treatment. Both technologies are under current expansion in Brazil. Large CEPT plants have been designed and built, up to 3.7 m3/s average design flow, as well as large UASB reactors, up to 3.0 m3/s average design flow. The applied technologies are cost-effective: they present low investment and efficiencies of BOD removal of up to 50% to 70%. They allow the plant construction in steps, an initial phase with efficiency over the usual primary treatment, and in order to achieve best effluent quality and meet legal water quality standards, a logic upgrade post-treatment can later on be implemented. The higher initial reduction of BOD and TSS also permits savings in construction and operational costs of secondary treatment, due to lower organic load and lower energy consumption. Sludge represents a particular point of attention: in the cases when the CEPT was used, Chemical Stabilisation of the Sludge (CSS) has also been practiced, eliminating the high construction costs of the digesters, all the plant staying chemically operated. In the cases when the UASB is used preceding secondary treatment, sludge can easily return to the anaerobic vessel, the costly sludge digestion unit being avoided. UASB reactors have practically no equipment in the anaerobic vessel, no energy consumption, low sludge production, and when applied in hot climates as in Brazil, heating devices are not required. The Brazilian experience, some particular cases, special comments on design and different secondary treatment processes are presented in this paper, as a contribution to the discussion of cost and benefits, a prime point to be considered.

Colour discharges are gaining renewed focus in the pulp and paper industry as increasingly strict regulatory limits are placed on wastewater quality and aesthetics. In-mill process improvements, such as ECF bleaching and oxygen delignification, have decreased wastewater colour loadings. However, a survey of 12 pulp and paper mill systems found that effluent treatment using aerated stabilisation basins (ASB) leads to average increases in colour of 20-40%. In some instances, this phenomenon may even double the influent colour levels. Activated sludge systems did not produce a colour increase. The measured increases that follow ASB secondary treatment may be sufficient for a mill to fail prescribed discharge standards. A detailed field survey focusing on sections of an integrated bleached kraft mill ASB treatment system was undertaken. The average increase in colour at the final point of discharge was 45%. The major changes in colour concentration occurred in the inlet to the main treatment pond, and in polishing ponds that followed the main treatment pond. Both of these areas receive little or no aeration. No significant change was observed in the highly aerated main pond. These results, along with literature reports, suggested that redox conditions play a major role in influencing colour behaviour. To test this, two series of paired continuously stirred reactors were used to treat whole mill effluent from two ECF bleached kraft mills in parallel. The first series initially treated under anaerobic conditions, followed by an aerobic reactor, while the second series reversed this order. With the initial anaerobic stage, effluent colour increased by 18% and 19% for the first and second series respectively. Subsequent treatment by aerobic bacteria further increased colour by 14% and 6%, for a total increase of 32% and 25%. Initial aerobic treatment, however, did not lead to any significant change in colour for either effluent. Further anaerobic treatment following aerobic conditions produced only small increases in colour. These results are consistent with the ASB and activated sludge system survey, suggesting that anaerobic conditions at the head of treatment systems initiate the observed increases in effluent colour in ASB treatment systems.

Among several applications of urban wastewater reuse, use of reclaimed wastewater to sustain stream flows has become attractive in the urban area. Since these rivers are used for recreational purposes and for restoring aquatic eco-system, the adequate control of residual chlorine is essential. Mathematical model for describing reactions between residual chlorine and organic matter in reclaimed wastewater has been developed. The model considers the effect of molecular weight distribution of organic matter on the reaction rate. Lab-scale experiments were performed to estimate reaction rates constants and to examine their temperature dependency. The experiments showed that 1) the smaller organic matter gave the larger reaction rate; 2) temperature effect on reaction rate was described by the Arrhenius formula; 3) decline of free chlorine had more temperature dependency than combined chlorine. The comparison of computed results with data from lab-scale experiments confirmed the validity of the model. We used the one-dimensional dispersion model with proposed reaction model and examined the seasonal variation of residual chlorine profile along the river sustained by reclaimed wastewater in Sapporo. Simulation showed that seasonal variation of nitrification performance in secondary treatment as well as change in temperature caused seasonal variation in residual chlorine profile along the river.

Combined sewer overflows (CSOs) have been recognised as one of the serious sources of pollution to the water environment during rain events, although field surveys to investigate the effect of their magnitude and duration on receiving waters have been very limited. The fates of enteric viruses (norovirus G1, G2, enteroviruses) and coliforms were determined in the wastewater treatment plant on a fine day and on a rainy day. Not all microorganisms were reduced in the primary treatment, but were reduced in the secondary treatment. Occurrences of enteric viruses and levels of coliforms were surveyed in the receiving coastal area after a CSO event, with the profiles of the enteric viruses in the coastal seawater being almost at the same positive ratio for 4 d after the CSO event.

Many cities need to build compact wastewater treatment plants because of lack of land. This paper discusses compact treatment methods. An enhanced primary treatment process based on coarse media filtration is analysed. A high-rate secondary wastewater treatment process has specifically been investigated, consisting of a highly loaded moving bed biofilm reactor directly followed by a coagulation and floc separation step. The objective with this high-rate process is to meet secondary treatment effluent standards at a minimum use of chemicals, minimum sludge production and minimum footprint. It is demonstrated that the biofilm in the bioreactor mainly deals with the soluble organic matter while coagulation deals with the colloidal matter. The bioreactor may, therefore, be designed based on the soluble COD loading only, resulting in a very compact plant when a compact biomass/floc separation reactor (i.e. flotation or direct filtration) is used. The paper reports specifically on the coagulant choice in flotation and filter run time in direct filtration.

Struvite deposition is a common problem in municipal wastewater treatment plants and can be signi?cant if not anticipated, but struvite deposits are completely manageable if properly addressed. This paper summarises experiences from a number of facilities that have dealt successfully with struvite problems, elaborates on the interrelations between secondary treatment and anaerobic digestion, and outlines an approach to control struvite and available alternatives.

In this paper coarse media filtration has been analysed as an alternative to the traditional settling in primary, secondary and tertiary treatment of wastewater. Various filter media configurations were evaluated for enhanced primary filtration. It was found that a dual media configuration based on Kaldnes biofilm media (K1 and K2modified) were most suitable when taking both separation efficiency as well as filter run time into consideration. SS removal efficiencies of around 75% were achieved in the dual Kaldnes primary filter at around 20 m/h without any chemical addition and around 85% at low dosage (1-2 mg/l) of a high MW cationic polymer FO4440SH. In the latter case COD was removed by around 70%. Further experiments were carried out on a multi-media Kaldnes-Filtralite-Sand (KFS) filter for enhanced primary treatment as well as for secondary filtration directly downstream of a high-rate moving bed biofilm reactor, resulting in an extremely compact secondary treatment process. The secondary KFS-filter gave SS-removal efficiencies around 90% (effluent SS < 15 mg/l) and filter run times of around 24 hrs at filtration rates of 10 m/h (sludge loading rates of around 1 kg /m2h) when a small dose (2 mg/l) of polymer was used. It is also demonstrated that the primary filter may also be utilised as a pre-denitrification reactor. A denitrification rate of 1.5 kg NO3-Nequiv./m3d was achieved when the filter was operated at a filtration rate of 5 m/h.

The Watercare Mangere Wastewater Treatment Facility, which treats wastewater from the greater Auckland New Zealand region, is undergoing a major expansion/upgrading to add advanced treatment and disinfection prior to discharge into a harbor. One important goal of this project is to protect the receiving water from microbial contamination. Since sufficient information on the fate of various microorganisms through wastewater treatment plants in New Zealand was not readily available, extensive pilot- and bench-scale studies were undertaken to develop specific design criteria for the treatment and disinfection systems. The specific objective of this study was to evaluate the removal and inactivation of enteric pathogens and other microbial indicators through treatment processes that employs UV irradiation as a final disinfection process. The removal of indicator organisms through secondary treatment was typically between 2.5-log (99.7% removal) and 2.8-log (99.8% removal) for fecal coliforms and enterococci, respectively. Indigenous F-specific bacteriophage exhibited a mean removal of 1.6-log (i.e. 97.7% removal) and Clostridium perfringens spores showed a mean removal of 1.3-log (i.e. 95% removal). The UV dose required to achieve a one log reduction in the concentration of indigenous F-specific bacteriophage was found to be approximately 20 mWs/cm2 per log removal. The concentration of enterovirus and adenovirus were consistently reduced to the limit of detection (1 TCID50/100L) at UV doses of 35 to 40 mWs/cm2 and 40 to 45 mWs/cm2, respectively. Clostridium perfringens spores were the most resistant indicator organisms, being reduced to less than 200 MPN/100 mL at a UV dose of 75 mWs/cm2.

In response to the European Union Urban Waste Water Directive, primary and secondary treatment is being installed at Birkenhead Treatment Works on the Wirral Peninsula in the North West of England. The 3.26 m diameter, 3.5 km long Great Culvert conduit currently conveys both river and sewage flow, and discharges these into the Mersey estuary. To avoid unnecessarily treating river flow, River Birket flow will be diverted directly into the Mersey estuary at the upstream end of the Great Culvert. Sewage flows remaining in the Great Culvert will be pumped to the Birkenhead Treatment Works, and treated before discharge to the Mersey. During extreme storm events, excessive river flows will be released into the Great Culvert and into the Mersey by weirs and penstocks. An innovative approach was taken to investigate, develop, and optimise a control strategy of various pumps, weirs, and penstocks in the Great Culvert, with the aim of minimising unscreened discharges and flooding. By combining hydraulic and dynamic control modelling into one study, implementation and commissioning times were reduced. In addition, by exhaustive testing, it was possible to demonstrate to the Environment Agency that all reasonable measures were being taken to minimise flooding in the upstream catchment and discharges to the Mersey.

Sublethal toxicity tests successfully measured the improved quality of pulp mill effluents from the first cycle of environmental effects monitoring (1992–1996) to the second cycle (1997–2000). Test endpoints showed notable shifts to higher concentrations (less toxic). During the second cycle of monitoring, significantly more tests showed no effect in full-strength effluent. Five case studies were considered as part of this exercise. Most of the improvement came with installation of secondary treatment. Twelve Ontario mills with secondary treatment showed reduced toxicity, compared to results with primary treatment. All 29 sets of sublethal data showed higher IC25s during the second cycle, and 23 of these differences were statistically significant. Any other changes between the two cycles of study caused only marginal overall improvement in toxicity, judging by 12 freshwater mills in British Columbia which had secondary treatment during both cycles. Sublethal tests successfully predicted the zone of potential effect in receiving water, agreeing with effects observed in biological surveys. Overlapping zones from multiple discharges could also be demonstrated. In a situation near Niagara Falls, sublethal tests estimated the proportions of toxic loading that four mills contributed to one water body. The prediction was realistic; the actual toxicity found for a mixed effluent was 57% of that predicted from separate toxicities. The conservative prediction agrees with the usual less-than-additive sublethal action of combined toxicants.

The Mediterranean climate of Central Portugal produces a bimodal precipitation pattern such that effluent dilution is high during the winter rainy period and low in summer. An integrated assessment strategy was used to investigate the effect of this seasonally distinct flow regime on the environmental effects of a largely eucalyptus-derived, bleached kraft mill effluent (BKME) that receives secondary treatment before discharge to the Vouga River. The assessment included the triad of various water chemistry measurements, laboratory bioassays, and field surveys of benthic invertebrate and periphytic diatoms. The BKME discharge increased water temperature, pH, colour, suspended solids, conductivity, chemical oxygen demand, plant nutrients (nitrogen and phosphorus) and AOX content in the downstream receiving waters during both seasons. However, differences were much more pronounced in summer during the natural low flow period. Ecotoxicity tests revealed a significant effluent effect only in summer. Attached diatoms exhibited reduced species diversity at effluent-affected sites only in summer. Invertebrate densities and diversity were reduced downstream of the effluent in both seasons, but more so in summer. The effluent discharge often increased downstream water temperature by 10 to 15°C, with summer temperatures regularly exceeding 30 to 35°C.

Arid areas call for imaginative water management solutions to avoid the dangers of water shortages. Growing demands of water for domestic and industrial uses decrease the availability of water for agriculture. It therefore becomes necessary to set up a policy for the use of domestic effluents. For the province of Mendoza, Argentina, with 1,500,000 inhabitants, a master plan was designed as of 1991 for the treatment of domestic effluents and subsequent disposal for irrigation. The guidelines set up by WHO for the use of wastewater in agricultural applications were taken into consideration. At present, the Province of Mendoza has available projects which are either complete, in execution or in the bidding process, entailing secondary treatment capacity with reuse of 320,000 cubic metres/day and an estimated possible irrigation area of 10,000 hectares. With this infrastructure, some strategic lines of action are recommended to establish a policy for the agricultural use of wastewater: (a) to program the use of treated wastewater to avoid discharges to irrigation flows; (b) to develop an institutional scheme for the efficient and safe use of these waters; and (c) develop scientific and technologic know-how to accompany the updated policies.

The sustainability of wastewater reclamation and reuse schemes is often limited by the increase in salt concentration that occurs with each water use. In this pilot study, we show that the cost of reclaiming wastewater and removing salt can be dramatically decreased by integrating recent advances in wastewater pond design, solids separation equipment, and membrane technology. Effluent from an AIWPS® Facility was clarified in a Krofta® SupracellTM Dissolved Air Flotation (DAF) unit and a Slow Sand Filter (SSF) prior to final treatment in an Expertise S.r.l. reverse osmosis (RO) unit. The ponds of the AIWPS® Facility removed an average of 82% of soluble BOD and 80% of soluble nitrogen. Following clarification, filtration, and RO treatment, the pollutant removals were > 99% for soluble BOD, > 99% for soluble nitrogen, and 98% for TDS. Based on membrane fouling rate data, the cleaning interval for the RO membranes in a full-scale AIWPS®-RO Facility would be over 100 days. This interval is on par with that typically seen in full-scale reclamation facilities treating secondary activated sludge effluent with microfiltration prior to reverse osmosis. A 4-MLD AIWPS®-RO Facility is expected to produce permeate water at substantially lower cost and lower energy consumption (US $698 and 443 kWh per million liters treated) than a system of equal capacity using conventional activated sludge secondary treatment followed by microfiltration and reverse osmosis (US $1274 and 911 kWh per million litres treated). This cost and energy differential is attributable to the lower capital and operating expenses of the AIWPS® Technology in comparison with activated sludge.