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The presence of active pharmaceutical ingredients (APIs) in the environment is of growing concern and effluents from wastewater treatment works (WwTWs) are one of the major sources. This research combines the outputs of a multimillion pound UK program of work to evaluate the fate of APIs in the wastewater treatment process. A combination of analysis of measured data and modelling has been applied to 18 APIs, representing a wide range of medicinal application and physico-chemical characteristics. Some isomers (for atorvastatin) and metabolites (for sertraline, carbamazepine and erythromycin) were also included. High variability was observed between removal rates for individual APIs between WwTW, which after statistical analysis could not be explained by the nominal WwTW process (e.g. activated sludge or trickling filter). Nor was there a clear relationship between API removal and physico-chemical parameters such as pKa, charge or log Kow. A publically available sewage process model, SimpleTreat 4.0 which has been rigorously validated and is now being used for exposure assessment with REACH legislation for organic chemicals and within the Biocidal Products Regulation by the European Medicines Agency for APIs, was used to estimate removal rates with which to compare with measured data. SimpleTreat provided estimates of removal rates within ±30% of observed values for the majority of the APIs measured, with the use of readily available WwTW specific parameters such as flow, total suspended solids and BOD data. The data and correlations provided in this study provide support for any future considerations regarding the management of API discharge to the aquatic environment. Unlabelled Image • Removal efficiency data for 19 pharmaceuticals and 4 metabolites in 45 UK sewage works • Activated sludge vs trickling filter works performance not significantly different • Removal not simply explained by phys-chem characteristics of pharmaceutical • Removal poorly correlated to sewage works sanitary determinands • SimpleTreat model capable of predicting removal to within 30% of measured values [ABSTRACT FROM AUTHOR]

Abstract Aerated Constructed Wetlands are a state-of-the-art design that provides a different physical and chemical environment (compared to traditional passive wetland designs) for the wastewater treatment processes and, thus, may have different pathogen removal characteristics. In order to establish the fate of bacterial and viral indicators, a field study was carried out at a Sewage Treatment Works (STW) in the UK (serving 20,000 pe). The STW consists of primary and secondary sedimentation tanks and trickling filters (TF) as the biological stage. A large (1,160 m2) pilot aerated Vertical Flow Constructed Wetland (AVFCW) was constructed at the STW as tertiary stage receiving ¼ of the total flow rate, i.e., 1250 m3/day. Effluent quality of the AVFCW complied with national and international standards for environmental discharge and reuse. For the first time, two sets of bacterial (Faecal coliforms, E.coli and intestinal enterococci) and viral indicators (Somatic coliphages, F -RNA specific bacteriophages and human-specific B. fragilis GB124 phages) were simultaneously investigated in an AVFCW and TF. High elimination rates were detected (up to 3.7 and 2.2 log reduction for bacteria indicators and phages, respectively) and strong correlations between the two sets were found. The superior efficiency of the aerated Constructed Wetlands in microbiological contamination removal compared to passive wetland systems was established for the first time, which may have implications for process selection for wastewater reuse. This field study therefore provides new evidence on the fate of bacteriophages and a first indication of their potential use for performance evaluation in TF and aerated Constructed Wetlands. It also demonstrates that the combination of TF with aerated constructed wetlands could be a novel and effective treatment scheme for new STW or for the upgrade of existing STW. Graphical abstract Unlabelled Image Highlights • Trickling filters and an experimental aerated Constructed Wetland were investigated. • Effluent quality below discharge legal limits even without a final disinfection step • 2–3.5log removal efficiency of three bacterial and three bacteriophages indicators • Strong correlations imply phages use as performance indicators in aerated wetlands. • Aerated Wetlands outperform passive systems in microbiological contamination removal. [ABSTRACT FROM AUTHOR]

The treatment of high-strength anaerobic digester effluent in laboratory-scale trickling filters for nitrification and then anaerobic filters for denitrification is reported. Five media types were investigated in the trickling filters: biochar, granular activated carbon (GAC), zeolite, Pall rings, and gravel. Three media were tested in five denitrifying filters: sand (S), bamboo wood chips (B), eucalyptus wood chips (E), bamboo with sand (B+S), and eucalyptus with sand (E+S). The different wood chips served as a supplemental electron donor for denitrification. From six months of operation, biochar, GAC, zeolite, Pall rings, and gravel media had turbidity (NTU) removal efficiencies of 90, 91, 77, 74, and 74%, respectively, and ammonia removal efficiencies of 83, 87, 85, 30, and 80%, respectively, which was primarily by nitrification to nitrate. For the anaerobic filters, S, B, B+S, E, and E+S had nitrate removal efficiencies of 30, 66, 53, 35, and 35%, and turbidity removal efficiencies of 88, 89, 84, 89, and 88%, respectively. Biochar and bamboo were selected as the best combination of media for trickling filter and anaerobic filter sequential treatment. Based on an average initial influent of 600 mg NH 3 -N L −1 , 50 mg NO 3 -N L −1 , and 980 NTU, the biochar filter's effluent would be 97 mg NH 3 -N L −1 , 475 mg NO 3 -N L −1 , and 120 NTU. The bamboo filter's final effluent would be 82 mg NH 3 -N L −1 , 157 mg NO 3 -N L −1 , and 13 NTU, which corresponds to 63% removal of total N and 99% removal of turbidity. These filter media thus present a simple option for sustainable post-treatment for nitrogen management and effluent polishing in low-resources settings. [ABSTRACT FROM AUTHOR]

The effects of floc structural characteristics, i.e. shape and dense biomass distribution, were evaluated on ultraviolet (UV) disinfection resistance, represented by the tailing level of the UV dose response curve (DRC). Ellipsoid-shaped flocs of similar volume and different projected circularities were constructed in-silico and a mathematical model was developed to compare their UV DRC tailing levels (indicative of UV-resistance). It was found that floc shape can significantly influence tailing level, and rounder flocs (i.e. flocs with higher circularity) were more UV-resistant. This result was confirmed experimentally by obtaining UV DRCs of two 75–90 μm floc populations with different percentages (20% vs. 30%) of flocs with circularities higher than 0.5. The population enriched in less circular flocs (i.e. 20% flocs with circularities >0.5) had a lower tailing level (at least by 1-log) compared to the other population. The second model was developed to describe variations in UV disinfection kinetics observed in flocs with transverse vs. radial biomass non-homogeneity, indicative of biofilm-originated vs. suspended flocs. The varied-density hemispheres model and shell-core model were developed to simulate transverse and radial non-homogeneity, respectively. The UV DRCs were mathematically constructed and biofilm-originated flocs showed higher UV resistance compared to suspended flocs. The calculated UV DRCs agreed well with the experimental data collected from activated sludge and trickling filter flocs (no fitting parameters were used). These findings provide useful information in terms of designing/modifying upstream processes for reducing UV disinfection energy demand. [ABSTRACT FROM AUTHOR]

The abundance of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) was investigated in full-scale two-stage trickling filters (TF) and moving bed bioreactor (MBBR) treating municipal wastewater. Biofilm samples were collected for 17 months from nitrifying TF (NTF), biochemical oxygen demand TF (BTF), and MBBR media. The abundance of AOA and AOB was determined using a quantitative PCR approach targeting the ammonia monooxygenase subunit A gene of archaea and bacteria. AOA were dominant in the NTF and MBBR, while AOB dominated in the BTF. AOA and AOB were more abundant during warmer months, and AOA were detected in the BTF only during warmer months. In laboratory nitrification activity experiments, ammonia oxidation to nitrite decreased when AOA populations from the NTF and MBBR were inhibited, demonstrating that AOA contributed to nitrification. This study has shown that AOA outnumber AOB and contribute to ammonia oxidation in full-scale nitrifying biofilm processes. [ABSTRACT FROM AUTHOR]

The present study develops membrane hybrid system for drinking water that combines a trickling filter (TF) and a thin-layer biosand filter (TBSF) prior to membrane. Two different types of trickling filter (submerged and protruding) were placed before the biosand filter (BSF) with two different sand depths (40 and 3 cm). The effectiveness of the TBSF was measured in terms of the reduction in levels of total organic carbon, turbidity, Escherichia coli, and bacteriophage MS2. The hybrid systems with a TF + BSF + MF membrane showed higher TOC removal and turbidity reduction than hybrid systems only with BSF + MF membrane. The TOC removal and turbidity reduction by the hybrid systems with a TF were much more stable than those of hybrid systems without a TF throughout the operating period despite the changing level of the TOC. The removal of E. coli by hybrid systems with a TF was greater (usually >99.99%) and more stable than that by the hybrid systems without a TF. However, the removal of bacteriophage MS2 by the hybrid systems with a TF was only moderate (~99%) and not greatly different from that by the hybrid systems without a TF. [ABSTRACT FROM AUTHOR]

Wastewater treatments are considered important means to control the environmental transmission of human norovirus (NoV). Information about NoV concentrations in untreated and treated effluents, their seasonality and typical removal rates achieved by different treatment processes is required to assess the effectiveness of sewage treatment processes in reducing human exposure to NoV. This paper reports on a characterisation of concentrations of NoV (genogroups I and II) in untreated sewage (screened influent) and treated effluents from five full scale wastewater treatment works (WwTW) in England. Results are shown for effluent samples characteristic of primary- (primary settlement, storm tank overflows), secondary- (activated sludge, trickling filters, humus tanks) and tertiary (UV disinfection) treatments. NoV occurrence in untreated sewage varied between years. This variation was consistent with the annual variation of the virus in the community as indicated by outbreak laboratory reports. Significant differences were found between mean NoV concentrations in effluents subject to different levels of treatment. Primary settlement achieved approximately 1 log 10 removal for both genogroups. Concentrations of NoV and Escherichia coli in untreated sewage were of the same order of magnitude of those in storm tank overflows. Of the secondary treatments studied, activated sludge was the most effective in removing NoV with mean log 10 removals of 3.11 and 2.34 for GI and GII, respectively. The results of this study provide evidence that monitoring of NoV in raw sewage or treated effluents could provide early warning of an elevated risk for NoV and potentially help prevent outbreaks through environmental exposure. They also provide evidence that elimination of stormwater discharges and improvement of the efficiency of activated sludge for NoV removal would be effective for reducing the risk of environmental transmission. [ABSTRACT FROM AUTHOR]

In many developing countries, inadequate access to safe drinking water is a major cause of morbidity and mortality. Furthermore, approximately 100 million people worldwide are exposed to arsenic (As) in drinking water. The World Health Organization is thus now encouraging the development and supply of a low-cost technology that can treat domestic water. The present study combined the use of a trickling filter (TF) with a biosand filter (BSF). Additionally, to remove As (V) from water, the use of the absorbents Fe–Mn–Si (FM-α) and zero-valent iron was experimentally investigated. Different compositions of influent were supplied in five stages. Efficiency was analyzed in terms of the total organic carbon, turbidity, UV 254 , As (V) content, flux, power consumption, total solids, and volatile solids of samples taken from four treatment systems (M-1: membrane, M-2: BSF + membrane, M-3: TF + membrane, and M-4: TF + BSF + membrane). Results show that the removal of organic matter and decline in flux over 45 d reduced in the order M-4 > M-2 > M-3 > M-1. The combination of TF, BSF, and M-4 was shown to have the most stable operation even under shock loading. The biofilm of the BSF and sieving effect played an important role in reducing the content of organic matter. The recovered flux of M-1 decreased and the M-1 membrane was backwashed four times. In comparison, M-3 required backwashing four times, M-2 required backwashing once, and M-4 did not require backwashing during operation. The M-4 system removed 95% of organic matter without any cleaning of the top soil throughout the experiment and reduced turbidity by 99%. Between systems M-1 to M-4, the most effective system was M-4 because of its stable operation without backwashing of the membrane throughout the experimental period. The M-2 system with FM-α embedded in the layers of sand removed 77% of As (V), while the M-4 system, using zero-valent iron adsorbents, removed 97% of As (V). [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the effects on treatment efficiency of oxidation–reduction (redox) conditions that are caused by different water saturation levels within vertical-flow constructed wetlands (VFCW), with specific attention to phosphorus (P) retention. The study was conducted by monitoring over 18 weeks a pilot-scale system consisting of a biological aerobic trickling filter as a biological pre-treatment step, followed by ferric chloride (FeCl 3 ) addition for phosphate removal and a stage of VFCW. By adjusting the water saturation level, the VFCW was operated successively under fully unsaturated, partly saturated, completely saturated (flooded), and then again unsaturated conditions. Redox potentials (Eh) were measured at three different levels within the VFCW. Results revealed that Eh was logically affected by the water-saturation level and the feeding–resting periods. Treatment efficiency was very good under fully unsaturated and partly saturated conditions. Under flooded conditions, the performance of the filter declined when the flood was maintained for around one week. However, VFCW regained its previous efficiency after the effluent was drained out and aerobic conditions were restored, indicating that the system was resistant and robust enough that periodical flooding did not affect its performance afterwards. [ABSTRACT FROM AUTHOR]

A study was conducted of treatment performance and nitrogen transformation processes in a trickling filter (TF) used to treat micro-polluted source water under variable hydraulic loading rates (HLRs), ranging from 1.0 to 3.0 m 3 /m 2 d. The TF achieved high and stable COD (97.7–99.3%) and NH 4 + -N (67.3–92.7%) removal efficiencies. Nitrification and anaerobic ammonium oxidation were the dominant nitrogen removal processes in the TF. Path analysis indicated that amoA /anammox and amoA /( narG + napA ) were the two key functional gene groups driving the major processes for NH 4 + -N and NO 2 − -N, respectively. The analysis also revealed that anammox/ amoA and nxrA /( nirK + nirS ) were the two key functional gene groups affecting processes associated with the NO 3 − -N transformation rate. The direct and indirect effect of functional gene groups further confirmed that nitrogen transformation processes are coupled at the molecular level, resulting in a mutual contribution to nitrogen removal in the TF. [ABSTRACT FROM AUTHOR]

To better understand pharmaceutical fate during wastewater treatment, analysis in both aqueous and particulate phases is needed. Reported herein is a multi-residue method for the determination of ten pharmaceutical drugs and the personal care product triclosan in wastewater matrices. Method quantitation limits ranged from 7.6 to 76.6 ng l − 1 for aqueous phases and from 7.0 to 96.7 ng g − 1 for particulate phases. The analytical method was applied to attain a complete process mass balance of a pilot-scale activated sludge plant (ASP) operated under controlled conditions. The mass balance (inclusive of aqueous and particulate concentrations at all sample points) was used to diagnose removal, revealing pharmaceuticals to be separable into three fate pathways: (a) biological degradation, (b) sorption onto activated sludge and (c) resistant to removal from the aqueous phase. These differences in fate behaviour explained a broad range of secondary removal observed (− 8 to 99%). The ASP was also simultaneously compared to a full-scale trickling filter (TF) works whilst receiving the same influent wastewater. Performance of the ASP and TF was similar, achieving total pharmaceutical removals of 253 and 249 μg g − 1 biochemical oxygen demand (BOD) removed, respectively. This corresponded with reductions in total pharmaceutical load of 91 and 90% (ANOVA, p - value > 0.05). Interestingly, despite low suspended solid concentrations final effluents of both the ASP and TF contained significant concentrations of some chemicals in the particulate phase. Individually, triclosan and the antibiotics ofloxacin and ciprofloxacin were within the particulate phase of effluents at concentrations ranging from 26 to 296 ng l − 1 . [ABSTRACT FROM AUTHOR]

The use of vertical flow constructed wetlands (VFCW) is growing rapidly in Europe for domestic wastewater treatment in small communities. In order to improve denitrification and dephosphatation as compared to classical VFCW, the Azoé-NP ® process has been developed. The process line consists of: a biological aerobic trickling filter as a primary treatment stage, ferric chloride (FeCl 3 ) addition for phosphorus (P) treatment and two stages of partially saturated VFCW. A municipal wastewater treatment plant using Azoé-NP ® process has been monitored during eight years through 44 campaigns of 24 h time-proportional inlet–outlet sampling followed by analyses of TSS, BOD 5 , COD, TKN, NO 3 –N and TP concentrations. The results revealed good performances of the overall treatment. To better characterize the performance of each treatment step, five additional 24 h monitoring campaigns were performed with samples taken from four different points along the treatment line. Results showed a good performance in dissolved carbon removal and nitrification by the trickling filter. The main part of the treatment was found to be done by filtration throughout the first filtration stage. Nitrate removal was achieved principally at the second filtration stage. Phosphorus migration through the first stage and its slight retention at the second stage was observed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thin iron scraps layer paved in the trickling filter enhanced the TP removal. [•] Zeolite trickling filter under intermittent water feeding benefits nitrification. [•] Coarse media in the first stage inhibits clogging of the latter infiltration stage. [•] Better influent dispersion for MSL was achieved owing to the two-stage design. [•] Two-stage filter system appeals to decentralized treatment of sewage well. [ABSTRACT FROM AUTHOR]

Abstract: Four trickling biofilter designs were assessed as low-energy alternatives to aerobic activated sludge (AS) for the treatment of personal care product industry wastes. The designs included partially submerged packed-media and sponge reactors with and without active aeration. Partial submergence was used to reduce active aeration needs. Simulated colourant wastes (up to COD=12,480mg/L, TN=128mg/L) were treated for 201days, including wastes with elevated oxidant levels. COD and TN removal efficiencies were always >79% and >30% (even without aeration). However, aerated sponge reactors consistently had the highest removal efficiencies, especially for TN (∼60%), and were most tolerant of elevated oxidants. This study shows sponge biofilters have great potential for treating colourant wastes because they achieve high treatment efficiencies and reduce energy use by >40% relative to AS systems. [Copyright &y& Elsevier]

Abstract: This work reports the degradation of nitrogen compounds in a commercial marine Recirculating Aquaculture System (RAS) aimed at the culture of sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). The annual production of fingerlings is around 18 million and the process includes a drum filter and a biological treatment in order to enhance the water quality. Ammonia measurements at the inlet of the biological system showed that the concentration of this compound followed a diurnal pattern closely related to the feeding of the fingerlings; thus every day after feeding around 8am, the concentration of ammonia started increasing, it reached a maximum about 8h after feeding and then continued decreasing until the following morning. With regard to nitrite concentration, no significant differences were observed between the values measured at the inlet and the outlet of the biological system during the day, with an average concentration of this compound ranging between 0.08 and 3.66mg NO2 −Nl−1. A drawback of ammonia removal by means of nitrification is the subsequent increase of nitrate as the final product of ammonia oxidation in the culture system. The nitrate concentration in the biofilters inlet was found to fluctuate between 22.33 and 55.44mg NO3 −Nl−1 during the characterization period. Partial water exchange was needed during the day in order to minimize the water losses during fish handling and to keep the concentration of nitrate below the maximum allowable level of 46mg NO3 −Nl−1 due to production requirements in the hatchery under study. The ammonia degradation within the biological system, obtained by the ammonia measurements and comparison of the values at the inlet and outlet of the trickling filters has been fitted satisfactorily to ½-order/0-order kinetic expressions in good agreement with the results found in literature for laboratory and pilot plant studies. Rate constants k (1/2-order) =0.49g1/2 m−1/2 day−1 and k (0-order) =0.64gm−2 day−1, have been obtained in this study for commercial trickling biofilters. Thus, this work reports for the first time the kinetics of ammonia oxidation in trickling biofilters installed in a commercial recirculating aquaculture marine water system. These results will provide useful information for the design of an appropriately sized biofilter in order to optimize the water quality and reduce the need to exchange water in this activity. [Copyright &y& Elsevier]

Abstract: This study examined the composition and structure of nitrifying biofilms sampled from a high-rate nitrifying trickling filter which was designed to pre-treat raw surface water for potable supply. The filter was operated under a range of feed water ammonia and organic carbon concentrations that mimicked the raw water quality of poorly protected catchments. The biofilm structure was examined using a combination of fluorescence in situ hybridisation and scanning electron microscopy. Biopolymers (carbohydrate and protein) were also measured. When the filter was operated under low organic loads, nitrifiers were abundant, representing the majority of microorganisms present. Uniquely, the study identified not only Nitrospira but also the less common Nitrobacter. Small increases in organic carbon promoted the rapid growth of filamentous heterotrophs, as well as the production of large amounts of polysaccharide. Stratification of nitrifiers and heterotrophs, and high polysaccharide were observed at all filter bed depths, which coincided with the impediment of nitrification throughout most of the filter bed. Observations presented here specifically linked biofilm structure with filter functionality, physically validating previous empirical modelling hypotheses regarding competitive interactions between autotrophic and heterotrophic bacteria in biofilms. [Copyright &y& Elsevier]

Abstract: This article analyses the relation between wastewater quality parameters and particle size distribution (PSD) in three real wastewater treatment plants with different biofilm technologies: submerged biofilter system, trickling filter system, and rotating biological contactor system. The main quality parameters, (suspended solids, turbidity and COD), and PSD in the influent and effluent water of each different biofilm treatment were analyzed during 1year. The PSD was fitted using the power law (n(d p)=∂N(d p)/∂d p = A·d p − b ·Log(d p )) obtaining the coefficients A and b to define the particle distribution. Mathematical correlations between this coefficients and the rest of parameters studied were found (SS=0.0713·A 0.585, turbidity=4.549×10−4·A 1.096, COD=0.0201·A 0.774). The relation with the average particle size by mass was also found, (d pma =60.3137·b −2.242). Moreover a relation between PSD and the particle elimination efficiency of the secondary treatment was study, (η =2.844–2.498·b relative +0.0863·A relative). These expressions are very useful to understand the behavior of the biofilm treatment system using PSD analyses. [Copyright &y& Elsevier]

Abstract: The nonwoven nanofibre membranes in this study are made by the electrospinning technique. With a diameter ranging from 80nm to several hundred nanometers, the nanofibres have a large surface area to volume ratio and a very high porosity. The aim of the study was to evaluate the use of nanofibre microfiltration membranes in three different membrane bioreactor (MBR) set-ups. More specific, in an active sludge MBR (AS-MBR), an AS-MBR with flux performing enhancer MPE50 and in a trickling filter MBR (TF-MBR). The results showed that the nanofibre membrane performed best with the TF-MBR. This was due to the removal of turbidity by the trickling filter, and also because of a new membrane module configuration. The flux was higher than the other configurations, and more important, the flux was stable for 85days after which the experiment was stopped. Also different cleaning techniques with 0.5% NaOCl and 0.2% HCl were tested and compared in this study. The nanofibre membrane structure and strengths were not affected after the procedures for cleaning. Scanning electron micrograph (SEM) pictures show the nanofibre membrane being clean after 12h of the alkali and acid treatment. [Copyright &y& Elsevier]

Abstract: This chapter describes the possibility to combine wastewater treatment in recirculating aquaculture systems (RAS) with the production of crop plants biomass. In an aquaponic RAS established in Waedenswil, Zurich, the potential of three crop plants was assessed to recycle nutrients from fish wastewater. A special design of trickling filters was used to provide nitrification of fish wastewater: Light-expanded clay aggregate (LECA) was filled in a layer of 30 cm in vegetable boxes, providing both surface for biofilm growth and cultivation area for crop plants. Aubergine, tomato and cucumber cultures were established in the LECA filter and nutrient removal rates calculated during 42–105 days. The highest nutrient removal rates by fruit harvest were achieved during tomato culture: over a period of >3 months, fruit production removed 0.52, 0.11 and 0.8 gm−2d−1 for N, P and K in hydroponic and 0.43, 0.07 and 0.4 gm−2d−1 for N, P and K in aquaponic. In aquaponic, 69% of nitrogen removal by the overall system could thus be converted into edible fruits. Plant yield in aquaponic was similar to conventional hydroponic production systems. The experiments showed that nutrient recycling is not a luxury reserved for rural areas with litlle space limitation; instead, the additionally occupied surface generates income by producing marketable goods. By converting nutrients into biomass, treating wastewater could become a profitable business. [Copyright &y& Elsevier]

Biological ammoniacal-nitrogen (NH4 +-N) and organic carbon (TOC) treatment was investigated in replicated mesoscale attached microbial film trickling filters, treating strong and weak strength landfill leachates in batch mode at temperatures of 3, 10, 15 and 30 °C. Comparing leachates, rates of NH4 +-N reduction (0.126–0.159 g m−2 d−1) were predominantly unaffected by leachate characteristics; there were significant differences in TOC rates (0.072–0.194 g m−2 d−1) but no trend relating to leachate strength. Rates of total oxidised nitrogen (TON) accumulation (0.012–0.144 g m−2 d−1) were slower for strong leachates. Comparing temperatures, treatment rates varied between 0.029–0.319 g NH4 +-N m−2 d−1 and 0.033–0.251 g C m−2 d−1 generally increasing with rising temperatures; rates at 3 °C were 9 and 13% of those at 30 °C for NH4 +-N and TOC respectively. For the weak leachates (NH4 +-N<140 mg l−1) complete oxidation of NH4 +-N was achieved. For the strong leachates (NH4 +-N 883–1150 mg l−1) a biphasic treatment response resulted in NH4 +-N removal efficiencies of between 68 and 88% and for one leachate no direct transformation of NH4 +-N to TON in bulk leachate. The temporal decoupling of NH4 +-N oxidation and TON accumulation in this leachate could not be fully explained by denitrification, volatilisation or anammox, suggesting temporary storage of N within the treatment system. This study demonstrates that passive aeration trickling filters can treat well-buffered high NH4 +-N strength landfill leachates under a range of temperatures and that leachate strength has no effect on initial NH4 +-N treatment rates. Whether this approach is a practicable option depends on a range of site specific factors. [Copyright &y& Elsevier]

Abstract: The interference of ammonia with chlorination is a prevalent problem encountered by water treatment plants located throughout South East Asia. The efficacy of high rate, plastic-packed trickling filters as a pre-treatment process to remove low concentrations of ammonia from polluted surface water was investigated. This paper presents the findings from a series of pilot experiments, which were designed to investigate the effect of specific conditions—namely low ammonia feed concentrations (0.5–5.0mgNH4-NL−1), variations in hydraulic surface load (72.5–145m3 m−2 d−1) and high suspended solid loads (51±25mgL−1)—on filter nitrifying capacity. The distribution of nitrification activity throughout a trickling filter bed was also characterised. Results confirmed that high hydraulic rate trickling filters were able to operate successfully, under ammonia-N concentrations some 10- to 50-fold lower and at hydraulic loading rates 30–100 times greater than those of conventional wastewater applications. Mass transport limitations posed by low ammonia-N concentrations on overall filter performance were insignificant, where apparent nitrification rates (0.4–1.6gNH4-Nm−2 d−1), equivalent to that of wastewater filters were recorded. High inert suspended solid loadings had no adverse effect on nitrification. Results imply that implementation of high rate trickling filters at the front-end of a water treatment train would reduce the ammonia-related chlorine demand, thereby offering significant cost savings. [Copyright &y& Elsevier]

Abstract: A pilot-scale trickling filter with dual layer support material was constructed and tested for simultaneous biological removal of ammonia, iron and manganese from potable water. The performance of the trickling filter was tested at constant hydraulic loading of 226m3/m2 d while feed concentrations of iron, ammonia and manganese were varied between 0.5 and 4.0, 0.5 and 3.0, and 0.5 and 1.3mg/l, respectively. The system was inoculated with a mixed culture and a series of experiments was performed to investigate the interactions among ammonia, iron and manganese removal when simultaneously present in the trickling filter. The oxidation reduction potential increased along the filter depth from about 150 to 600mV, depending on the feed concentrations, thus enabling one-stage simultaneous removal of the three pollutants. Ammonia and iron drastically affected manganese oxidation and manganese was found to be the rate-limiting pollutant. The results are presented using an operating diagram of the system, that determines the range of operating conditions resulting in optimal operation, keeping iron, ammonia and manganese concentration under the maximum permitted limits in potable water. [Copyright &y& Elsevier]

Abstract: Two pilot-scale trickling filters were constructed and tested for manganese removal from potable water, using different fractions of silicic gravel as support media (mono- and multilayer filter). Manganese oxidation in drinking water was found to be cause by both biological oxidation and heterogeneous catalytic paths. Mixed culture populations were used to inoculate the trickling filters and the feed manganese concentrations and volumetric flow rates (VFRs) were between 0.6–2.0mg/l and 500–2000ml/min, respectively. The monolayer filter was flooded for high VFRs, and it was very effective for all conditions tested (100% removal efficiency, up to 2850mgMn/day). The multilayer filter was less effective for high manganese concentrations but it could remove up to 3250mgMn/day. A new mathematical model was developed assuming heterogeneous autocatalytic and biological as the main oxidation manganese paths. First order kinetics was used to describe the heterogeneous catalytic oxidation, while Monod-type kinetics was used to describe the net biological manganese oxidation. The simplicity of the pilot-scale design, the lack of need for an external mechanical aeration source and the ability to predict operation of the system offers a very attractive solution for manganese removal from potable water. [Copyright &y& Elsevier]

Abstract: The main constraint in lagoon treatment is the high suspended solids (SS) in the effluents, which is primarily due to high concentrations of algal cells in the finished effluent. The objective of this study was to remove turbidity originating from algae present in oxidation pond effluents by an easy and inexpensive method. For this reason, a novel lab-scale step feed dual treatment (SFDT) process was developed and the effectiveness of the trickling filter (TF) unit within the system in removing algae and organic matter was investigated. The SFDT process developed in this study is a unique and inexpensive way to scavenge algae from oxidation pond effluents. As opposed to earlier and somewhat unsuccessful studies where pond effluent post treatment was tested on oncethrough trickling filters, in this study pond effluents were directed to a step fed TF, so as to provide a dual treatment. Step feeding provided the necessary substrate to maintain a biofilm in TF, thereby affecting organic particles interception. The stabilization pond was not simulated in the study since the main focus was on the behaviour of the TF unit. The hydraulic loading rate (HLR) (0.5–2–4 m3/m2 day), influent COD (150–550 mg/L) and influent Chl-a concentrations (250–600 μg/L) were selected as operational variables. It was observed that, in general, removal percentages for turbidity, Chl-a, SS and COD increased considerably with the decreasing HLR, such as the removal efficiency of Chl-a was increased from 89.4% to about 97% when HLR was decreased from 4 m3/m2 day to 2 m3/m2 day. As a result, trickling filter produced clear effluents, with less than 2 NTU and the removal efficiency of turbidity being higher than 88%, and also removal percentages for Chl-a were higher than 95% for most of the cases. [Copyright &y& Elsevier]

Two pilot-scale trickling filters were used in order to estimate Cr(VI) reduction through biological mechanisms in biofilm reactors operated in SBR mode with recirculation using different filter media types, i.e. plastic media and calcitic gravel. The feed concentrations of Cr(VI) examined were about 5, 10, 20, 30, 50 and 100mg/l, while the concentration of the organic carbon was constant at 400mg/l, in order to avoid carbon limitations in the bulk liquid. Maximum reduction rates of 4.8 and 4.7gCr(VI)/d were observed for feed Cr(VI) concentration of about 5mgCr(VI)/l, for the filters with the plastic support material and the gravel media, respectively. The reduction rates were significantly affected by the feed Cr(VI) concentration in both bioreactors. A dual-enzyme kinetic model was used in order to describe Cr(VI) reduction by aerobically grown mixed cultures. Model predictions were found to correspond very closely to experimental quantitative observations of Cr(VI) reduction at both pilot-scale trickling filters used. [Copyright &y& Elsevier]

Abstract: Pilot scale trickling filters were constructed and tested in order to study biological removal of ammonia, iron and manganese from potable water. The effect of the size of the support material on nitrification performance was studied extensively. The mean size of the gravel and hence, the specific surface area was found to be critical for optimal nitrification operation. A steady-state model developed in previous work was used to predict filter''s performance. The model was very accurate only for the gravel size for which maximum nitrification rates were observed. The effect of the operational conditions on the physico-chemical and combined physico-chemical and biological iron oxidation was also studied. It was found that the contribution of biological oxidation is significant, increasing filter''s efficiency by about 6% and reducing the required filter depth by about 40%. Manganese biological removal was studied using gravel with small mean diameter, thus providing high specific surface area. Feed concentrations up to 4.0 mg/l were treated sufficiently. Finally, experiments were performed to investigate the simultaneous removal of ammonia, iron and manganese. Experimental results showed that the combined, as well as the simultaneous removal of the aforementioned pollutants, can be achieved by single-step filtration. [Copyright &y& Elsevier]

Abstract: Fifty-nine stream-water samples and 14 municipal wastewater treatment facility (WWTF) discharge samples in Johnson County, northeastern Kansas, were analyzed for 55 compounds collectively described as organic wastewater compounds (OWCs). Stream-water samples were collected upstream, in, and downstream from WWTF discharges in urban and rural areas during base-flow conditions. The effect of secondary treatment processes on OWC occurrence was evaluated by collecting eight samples from WWTF discharges using activated sludge and six from WWTFs samples using trickling filter treatment processes. Samples collected directly from WWTF discharges contained the largest concentrations of most OWCs in this study. Samples from trickling filter discharges had significantly larger concentrations of many OWCs (p-value<0.05) compared to samples collected from activated sludge discharges. OWC concentrations decreased significantly in samples from WWTF discharges compared to stream-water samples collected from sites greater than 2000 m downstream. Upstream from WWTF discharges, base-flow samples collected in streams draining predominantly urban watersheds had significantly larger concentrations of cumulative OWCs (p-value=0.03), caffeine (p-value=0.01), and tris(2-butoxyethyl) phosphate (p-value<0.01) than those collected downstream from more rural watersheds. [Copyright &y& Elsevier]

Abstract: The aim of this work was to assess the effectiveness of a biological trickling filter for the treatment of wastewaters produced by a company manufacturing organic dyes and varnishes. The combined wastewater effluent was fed to a pilot-scale trickling filter in two feeding modes, continuously and as a sequencing batch reactor (SBR). The biodegradability of the diluted wastewaters that were subjected to physicochemical treatment, using Ca(OH)2 and FeSO4, was initially studied using a continuously operated trickling filter. The system efficiency ranged up to 60–70% for a hydraulic loading of 1.1m3/m2 day and up to 80–85% for a hydraulic loading 0.6m3/m2 day. A stable chemical oxygen demand (COD) removal efficiency of 60–70% was achieved even in the case of undiluted wastewater at a hydraulic loading of 1.1m3/m2 day. The effectiveness of biological treatment of a mixture of the company''s main wastewater streams was also examined. The microorganisms developed in the trickling filter were able to efficiently remove COD levels up to 36,000mg/L, under aerobic conditions at pH values between 5.5 and 8.0. Depending on the operating conditions of the system, about 30–60% of the total COD removal was attributed to air stripping caused by the air supply at the bottom of the filter, whereas the rest of the COD was clearly removed through biological action. The proposed biological treatment process based on a trickling filter, which was operated either continuously or even better in an SBR mode, appears as a promising pretreatment step for coping with dye manufacturing wastewaters in terms of removing a significant portion of the organic content. [Copyright &y& Elsevier]

Abstract: A pilot-scale trickling filter was constructed and tested for iron removal from potable water. Iron removal was found to be caused by both biological and physico-chemical iron oxidation. The extent of each oxidation type was assessed. The system was inoculated with mixed culture and its performance was tested under continuous operation at 14°C. Feed iron concentrations and volumetric flow rates (VFR), ranged between 1–4mg/l and 1000–3000ml/min (225–680m3/m2day), respectively. First order kinetics was used to describe the physico-chemical iron oxidation while Monod-type kinetics was used to describe the net biological iron oxidation. An increase of VFR from 1000 to 3000ml/min reduced the filter''s physico-chemical removal efficiency from 93 to 80%, while it remained constant for all the iron feed concentrations (1–4mg/l) that were tested at each VFR. Bio-oxidation improved filter efficiency by about 5–6%. In all cases there was very good agreement between model predictions and experimental data. A series of experiments were also performed in order to investigate the simultaneous ammonia and iron oxidation. It was found that ammonia influence on iron removal becomes substantial only for high iron and ammonia concentrations. The simplicity of the pilot-scale design, the lack of the need for an external mechanical aeration source and the ease for the design and prediction of the system operation offers a very attractive solution for iron removal from potable water. [Copyright &y& Elsevier]

Abstract: This review deals with the main mechanisms and parameters affecting design and performance of trickling filters in aquaculture. Relationships between nitrification rates and easily accessible process parameters, like bulk phase concentration of TAN, O2, organic matter (COD), nitrite, temperature, HCO3 −, pH and the hydraulic loading of the trickling filter, are discussed in relation to the design and operation of such filters. Trickling filter design procedures are presented and one of them, a model describing the nitrification performance of trickling filters by plug-flow characteristics, is discussed in greater detail. Finally, practical aspects in relation to filter design and operation are presented. [Copyright &y& Elsevier]

Abstract: A pilot-scale trickling filter was constructed and tested for biological chromium(VI) removal from industrial wastewater. Indigenous bacteria from industrial sludge were enriched and used as inoculum for the filter. Sodium acetate was used as carbon source and it was found to inhibit chromate reduction at high concentrations. Three different operating modes were used to investigate the optimal performance and efficiency of the filter, i.e. batch, continuous and SBR with recirculation. The latter one was found to achieve removal rates up to 530g Cr(VI)/m2 d, while aeration was taking place naturally without the use of any external mechanical means. The low operating cost combined with the high hexavalent chromium reduction rates indicates that this technology may offer a feasible solution to a very serious environmental problem. [Copyright &y& Elsevier]

The performance of a hybrid reactor, comprising of trickling filter and activated sludge process, in treating nitrobenzene wastewater was investigated. Acetate induced cells of mixed consortia was acclimatized with gradual increase of nitrobenzene concentration up to 90 mg/l in 100 days using sodium acetate as co-substrate and considering COD and nitrobenzene concentration as paramount parameters for assessing the growth of biofilm and acclimation. A removal of 60–95.80% COD and 80–90.23% nitrobenzene was observed during acclimation. During hydraulic retention time (HRT) studies, the optimum HRT was found to be 29.55 h at which a maximum of 95.83% COD and 97.93% nitrobenzene removal was observed. Other studies included optimization of C:N ratio, substrate:co-substrate ratio, effect of shock loading and estimation of volatilization losses. The optimum C:N ratio was found to be 100:20 at which maximum 97.93% removal of nitrobenzene was observed. At optimum HRT (29.55 h) and optimum C:N ratio (100:20) optimum substrate:co-substrate ratio was found to be 1:33. From the shock load studies it can be concluded that the system can withstand shock load up to two times of usual nitrobenzene concentration. A loss of 9.44% nitrobenzene was observed due to volatilization and mass balance gave an efficiency of 87.49% biological removal of nitrobenzene. [Copyright &y& Elsevier]

Biofilm samples from a carbonaceous trickling filter (TF) were evaluated in bench scale reactors to determine their maximum potential denitrification rates. Intact, undisturbed biofilms were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent spiked with nitrate to a final concentration of 16–18 mg/L as N. Dissolved oxygen concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase. Nitrate loss from the reactors was monitored over a 5 h period. Denitrification rates of 3.09–5.55 g-N/m2 day were observed with no initial lag period. This suggests that the capacity for denitrification is inherent in the biofilm and that denitrification can take place even when oxygen is present in the bulk aqueous phase. There were no significant differences in denitrification rates per unit area of media (g–N/m2 day) either between (a) experimental runs or (b) sampling locations over the trickling filter. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, this approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification. [Copyright &y& Elsevier]

• The two monitored WWTPs had a high daily variability in N 2 O emissions. • The seasonal variability of N 2 O emissions was also significant and correlated to the influent N loads (AS) and wastewater temperatures (TF). • The average N 2 O EF determined for the WWTP-1 AT (0.04 %) and WWTP-2 TF (0.005 %) were substantially lower than the N 2 O EF (1.6 %). Monitoring of nitrous oxide (N 2 O) emissions from wastewater treatment plants (WWTP) correlated to different operational conditions plays an important role in proposing mitigation strategies. However, few full-scale studies are available so far correlating N 2 O emission factors (EF) from wastewater treatment systems to different structural, operational and environmental configurations. In this context, the aim of this study was to evaluate the variability of N 2 O emissions from two aerobic treatment systems, activated sludge (AS) and low-rate trickling filter (TF), operated as post-treatments in upflow anaerobic sludge blanket reactors (UASB), under different operational conditions: (1) employed aeration system, (2) biomass growth and (3) environmental conditions, with a main focus on the generation of N 2 O EFs for these types of systems. Both studied systems displayed high temporal variability in N 2 O emissions associated with different operational and environmental conditions, such as: (1) aeration intermittency and high amplitudes of influent N loads for the AS system, (2) recirculation of treated wastewater and different wastewater temperatures for the TF system. In addition, the temporal variability of methane (CH 4) emissions was also significant, with greater amplitudes for the AS system, due to the greater air-stripping effect intensified by the combination of intermittency and excess aeration. Finally, regardless of the employed operational condition, the average EFs (N 2 O and CH 4) determined for the WWTP-1 aeration tank (AT) (0.04 % and 0.054 %) and WWTP-2 TF (0.005 % and 0.015 %) were substantially lower than the N 2 O and CH 4 EFs (1.6 % and 0.75 %) suggested by the IPCC, for centralized WWTPs with aerobic systems. [ABSTRACT FROM AUTHOR]

• COD removal efficiency of BES-based TF reactor reached 97% at 1.0 g-COD/L/day. • Effluent TN discharge was <113 mg/L and below legal limit of 120 mg/L/day. • Geobacter caused current generation in biofilms with columbic efficiency of 11%. • Bacterial groups for COD decomposition, nitrification, and denitrification found. • One-step reactor treats wastewater with energy efficiency and no sludge production. A bioelectrochemical system (BES)-based trickling filter (TF) reactor was utilized for wastewater treatment. At a COD load of 1.0 g-COD/L/day, effluent chemical oxygen demand (COD) and total nitrogen (TN) were 115 and 108 mg/L, respectively, which were allowed for discharge. Superior performance was achieved at 0.5 g-COD/L/day with a circulation rate of 8 L/h, and both COD and TN removal were >98%. Coulombic efficiency was 11% at 1.0 g-COD/L/day and at most 16% at 0.5 g-COD/L/day. COD removal decreased when the BES was removed, demonstrating that BES improved COD removal capability. In anodic biofilms, exoelectrogenic, facultative, nitrifying, and sulfate-reducing bacteria could coexist. Geobacter for current generation grew inside the biofilm, and bacteria in the middle and outer layers consumed oxygen and degraded organic matter and nitrogen. This BES-based TF reactor may be used for efficient and cost-effective COD and TN removal at high loads without excess sludge removal. [ABSTRACT FROM AUTHOR]

There is a great need for simple methods for digestate management for potential household sanitation systems based on anaerobic digestion of minimally diluted fecal waste in countries that lack safe sanitation. Herein, a full-scale three-stage filter for nitrogen and phosphorus removal from anaerobic digester effluent was implemented in Madagascar. It included a trickling filter with crushed charcoal (for aerobic nitrification), a submerged anaerobic filter with bamboo chips (for denitrification), and a submerged filter with scrap iron (for phosphorus removal). All filter materials were sourced locally. Three parallel replicate systems were operated in two sequential 8-week phases for a total of 16 continuous weeks. Though the influent feed was not as expected, with much of nitrogen in the feed coming in as organic N and not as NH 3 –N, the filters still removed 38–49% of total incoming nitrogen. The filters achieved high rates of nitrogen transformation along with removing solids (73–82% turbidity removal), chemical oxygen demand (67–75% removal), and phosphorus (31–50% removal). Overall, the reaction rates from this full-scale study were in line with previous lab-scale investigations with scaled-down systems, supporting their application in real-world scenarios. Based on this study, simple effluent filters can support nutrient removal for small-scale and onsite fecal sludge treatment systems. Image 1 • High-strength anaerobic digester effluent was treated in three-stage filters. • Full-scale filters were constructed in Madagascar using all local materials. • Crushed charcoal trickling filters achieved nitrification rates up to 0.13 kg N m−3 d−1. • Bamboo woodchip filters achieved denitrification rates up to 0.03 kg N m−3 d−1. • Scrap iron filter removed 126 g P m−3 d−1 with 23.2 g P kg−1 Fe capacity. [ABSTRACT FROM AUTHOR]

• COD removal rate could reach 92.1% with initial COD concentration of 960 mg/L. • Acclimation of the microorganism led to high removal efficiency of nitrogen. • AMS activity and protein content in EPS could be fit by quadratic function model. • A peak was identified as active substances in 3-D EEM diagram. • SDBS inhibited the transport and metabolisms of amino acids, carbohydrate and lipids. Sequential vertical flow trickling filter and horizontal flow multi-soil-layering bioreactor were investigated for the treatment of decentralized domestic wastewater at various concentrations of sodium dodecyl benzene sulfonate (SDBS). Results have shown that the removal rate of COD could reach 92.1% at initial COD concentration of 960 mg/L (800 mg/L was provided by SDBS). NH 4 +-N concentration could be reduced from 52.4 to 9.71 mg/L without aeration. Besides, a quadratic function model was fit to describe the relationship between the relative activity of amylase and the protein content in extracellular polymer substance. SDBS could inhibit the transport and metabolisms of amino acids, lipids and carbohydrates in biofilms. The analysis of three-dimensional fluorescence diagram indicated that the peak in excitation/emission wavelengths = 310–340/370–430 nm was the characteristic peaks of some active substances such as some enzymes in EPS. Only Microbacterium could totally offset the toxicity of SDBS degradation products. [ABSTRACT FROM AUTHOR]