Occurrence and fate of emerging wastewater contaminants in Western Balkan Region

This paper reports on a comprehensive reconnaissance of over seventy individual wastewater contaminants in the region of Western Balkan (WB; Bosnia and Herzegovina, Croatia and Serbia), including some prominent classes of emerging contaminants such as pharmaceuticals and personal care products, surfactants and their degradation products, plasticizers, pesticides, insect repellents, and flame retardants. All determinations were carried out using a multiresidue analytical approach, based on the application of gas chromatographic and liquid chromatographic techniques coupled to mass spectrometric detection. The results confirmed a widespread occurrence of the emerging contaminants in municipal wastewaters of the region. The most prominent contaminant classes, determined in municipal wastewaters, were those derived from aromatic surfactants, including linear alkylbenzene sulphonates (LAS) and alkylphenol polyethoxylates (APEO), with the concentrations in raw wastewater reaching into the mg/l range. All other contaminants were present in much lower concentrations, rarely exceeding few microg/l. The most abundant individual compounds belonged to several classes of pharmaceuticals (antimicrobials, analgesics and antiinflammatories, beta-blockers and lipid regulators) and personal care products (fragrances). Due to the rather poor wastewater management practices in WB countries, with less than 5% of all wastewaters being biologically treated, most of the contaminants present in wastewaters reach ambient waters and may represent a significant environmental concern.     

Occurrence, partition and removal of pharmaceuticals in sewage water and sludge during wastewater treatment

During 8 sampling campaigns carried out over a period of two years, 72 samples, including influent and effluent wastewater, and sludge samples from three conventional wastewater treatment plants (WWTPs), were analyzed to assess the occurrence and fate of 43 pharmaceutical compounds. The selected pharmaceuticals belong to different therapeutic classes, i.e. non-steroidal anti-inflammatory drugs, lipid modifying agents (fibrates and statins), psychiatric drugs (benzodiazepine derivative drugs and antiepileptics), histamine H2-receptor antagonists, antibacterials for systemic use, beta blocking agents, beta-agonists, diuretics, angiotensin converting enzyme (ACE) inhibitors and anti-diabetics. The obtained results showed the presence of 32 target compounds in wastewater influent and 29 in effluent, in concentrations ranging from low ng/L to a few μg/L (e.g. NSAIDs). The analysis of sludge samples showed that 21 pharmaceuticals accumulated in sewage sludge from all three WWTPs in concentrations up to 100 ng/g. This indicates that even good removal rates obtained in aqueous phase (i.e. comparison of influent and effluent wastewater concentrations) do not imply degradation to the same extent. For this reason, the overall removal was estimated as a sum of all the losses of a parent compound produces by different mechanisms of chemical and physical transformation, biodegradation and sorption to solid matter. The target compounds showed very different removal rates and no logical pattern in behaviour even if they belong to the same therapeutic groups. What is clear is that the elimination of most of the substances is incomplete and improvements of the wastewater treatment and subsequent treatments of the produced sludge are required to prevent the introduction of these micro-pollutants in the environment.     

Occurrence and implications of estrogens and xenoestrogens in sewage effluents and receiving waters from South East Queensland

We report a survey on the occurrence of estrogens (estrone, E1; 17β-estradiol, E2; 17α-ethynylestradiol, EE2) and xenoestrogens (bisphenol-A, BPA; 4-t-octylphenol, 4-t-OP; 4-nonylphenols, 4-NP; and nonylphenol mono- and di-ethoxylates, NPE1 and NPE2) in effluents from five wastewater treatment plants and their receiving waters in South East Queensland. The total xenoestrogen concentrations in effluent ranged between 2446 ng/L and 6579 ng/L, with 4-NP and NPE1-2 having much higher concentration levels than BPA and 4-t-OP. The estrogen levels in effluent varied from 9.12 to 32.22 ng/L for E1, from 1.37 ng/L to 6.35 ng/L for E2 and from 0.11 ng/L to 1.20 ng/L for EE2. No significant differences (p < 0.05) in the concentrations of the selected estrogenic compounds were found for the effluents from the five sewage treatment plants. The estrogens and xenoestrogens were also found in the receiving waters at relatively lower concentration levels due to dilution of effluents in the rivers. Based on the chemical analysis data and relative potency of the compound from in vitro and in vivo bioassays from the literature, the calculated in vitro EEQ values (estrogen equivalents) in the receiving river waters downstream of the effluent discharge points ranged from 1.32 to 11.79 ng/L, while the in vivo EEQ values (vitellogenin response in rainbow trout) ranged from 2.48 to 21.18 ng/L. The three estrogens accounted for the majority of the EEQ in the water samples. This study indicates that the rivers of South East Queensland are at potential risk.     

Battery industry wastewater: Pb removal and produced sludge

The process of neutralization with NaOH, in the presence of Fe(III) salt, of sulphuric acid battery industry wastewater seems to be more suitable than any other process for Pb removal because at the same time, it allows the exploitation of the scavenger action of Fe(III), which is often present in the same wastewater and precipitates as hydroxides. In order to optimize sludge production, a laboratory research study has been carried out to minimize the quantity of Fe(III) to be added. All aspects concerning the chemistry of wastewater have been taken into consideration step by step and discussed. As a result, a process which requires the addition of Fe(III) so that an Fe/Pb ratio, both expressed as ppm, of the order of 0.5 is achieved. The process has been applied to two artificial solutions, characterized by a content of H₂SO₄ of 1000 and 5000 ppm, respectively, and by 10 ppm of Pb, as well as to five samples of wastewater. The proposed process takes about 1 h to perform: 30 min for neutralization up to pH 8.5–9.5 and Fe(III) addition and 30 min for correction in the 9–9.5 pH range and for flocculation with the help of a polyelectrolyte. The Pb concentration of the treated effluent is below 0.2 ppm. Conditions for Pb removal using only NaOH or Na₂CO₃ have also been considered.     

Occurrence and fate of TMDD in wastewater treatment plants in Germany

The occurrence and fate of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD) was investigated in four wastewater treatment plants (WWTPs) in Germany. The concentration of TMDD in influents and effluents in the WWTPs ranged from 134 ng/L to 5846 ng/L and from <LOQ to 3539 ng/L correspondingly. Loads determined in influents (10.1 g/d-1142 g/d) and effluents (<LOQ - 425 g/d) indicate that TMDD is partially removed from the wastewater. The elimination rates varied between 33% and 68%. Based on the load analysis, the TMDD effluent discharge of WWTPs investigated varied from 8.29 kg/a to 52.6 kg/a. Day and week profiles were recorded and indicated that TMDD is introduced into the sewage through household and indirect dischargers with high fluctuations. Seasonal variations in the TMDD loads were also analyzed in three of the studied WWTPs. One of the WWTPs demonstrated statistically higher TMDD loads during the warm period (164 g/d) than during the cold period (91.3 g/d), for the others WWTPs any differences could not be established. The input of TMDD during weekends and working days was also studied. The results did not show any significant trend of TMDD discharge into the WWTPs.     

Diurnal variations in the occurrence and the fate of hormones and antibiotics in activated sludge wastewater treatment in Oslo, Norway

We present an assessment of the dynamics in the influent concentration of hormones (estrone, estriol) and antibiotics (trimethoprim, sulfamethoxazole, tetracycline, ciprofloxacin) in the liquid phase including the efficiency of biological municipal wastewater treatment. The concentration of estradiol, 17-α−ethinylestradiol, doxycycline, oxytetracycline, demeclocycline, chlortetracycline, cefuroxime, cyclophosphamide, and ifosfamide were below the limit of detection in all of the sewage samples collected within this study. Two different types of diurnal variation pattern were identified in the influent mass loads of selected antibiotics and hormones that effectively correlate with daily drug administration patterns and with the expected maximum human hormone release, respectively. The occurrence of natural hormones and antimicrobials, administered every 12 hours, shows a daily trend of decreasing contaminant mass load, having the maximum values in the morning hours. The occurrence of antibiotics, typically administered every 8 hours, indicates a daily peak value in samples collected under the highest hydraulic loading. The efficiency of biological removal of both hormones and antibiotics is shown to be limited. Compared to the values obtained in the influent samples, increased concentrations are observed in the biologically treated effluent for trimethoprim, sulfamethoxazole and ciprofloxacin, mainly as a result of deconjugation processes. Ciprofloxacin is shown as the predominant antimicrobial compound in the effluent, and it is present at quantities approximately 10 fold greater than the total mass of the other of the compounds due to poor removal efficiency and alternating solid-liquid partitioning behaviour. Our results suggest that, to increase the micro-pollutant removal and the chemical dosing efficiency in enhanced tertiary treatment, significant benefits can be derived from the optimisation of reactor design and the development of control schemes that accounts for diurnal secondary effluent micro-pollutant and hydraulic loading patterns.     

Occurrence and fate of quinolone and fluoroquinolone antibiotics in a municipal sewage treatment plant

This study developed a method for analysis of nineteen quinolone and fluoroquinolone antibiotics (FQs) in sludge samples, and investigated the occurrence and fate of the FQs in a municipal sewage treatment plant (STP) with anaerobic, anoxic, and aerobic treatment processes. Eleven compounds, including pipemidic acid, fleroxacin, ofloxacin, norfloxacin, ciprofloxacin, enrofloxacin, lomefloxacin, sparfloxacin, gatifloxacin, moxifloxacin, and sarafloxacin (only in sludge), were detected in the STP. The predominance of ofloxacin and norfloxacin, followed by lomefloxacin, ciprofloxacin, gatifloxacin, and moxifloxacin, were found in wastewater, suspended solids, and sludge. The total concentrations of FQs were 2573 ± 241 ng/L, 1013 ± 218 ng/L, and 18.4 ± 0.9 mg/kg in raw sewage, secondary effluent, and sludge, respectively. Extremely low mass change percentages were observed for FQs in anaerobic, anoxic, and aerobic treatment units, suggesting biodegradation to be of minor importance in the removal of FQs in STPs. 50-87% of the initial FQs loadings (except for pipemidic acid (36%)) were ultimately found in the dewatered sludge. Mean removal efficiencies of FQs in the STP were 56-75%, except for new generation drugs such as moxifloxacin (40 ± 5%) and gatifloxacin (43 ± 13%). A significant positive correlation was found between removal efficiencies and K_d of FQs. The major factor in the removal of FQs in the STP was sorption to sludge, which was not governed by hydrophobic interactions. The long-term cycling and persistence of FQs in the STP has made activated sludge as a huge reservoir of FQ antibiotics.     

ICEAS工艺启动及活性污泥培养驯化应用实例

结合福州市金山污水处理厂工艺及及活性污泥培养驯化实例,分析总结ICEAS工艺启动及活性污泥培养驯化经验。     

Source identification of heavy metals in sewage sludge and the effect of influent characteristics: a case study from China

To advance the reclamation of sewage sludge and evaluate the potential risk during sludge application, wastewater and sludge were sampled from seven secondary wastewater treatment plants seasonally in 2016 and 2017. The influent characteristics and the accumulation of eight toxic heavy metals in sludge were analyzed. According to the results, copper, chromium, nickle and zinc were the main heavy metals constraining reclamation of sewage sludge in Shanghai and they were mainly from domestic wastewater. Influent concentration, treatment process and coexisting elements had significant effects on accumulation of heavy metals in sludge. Lead concentration in sludge from AAC plants was generally higher than that from AAO plants, but for other metals the differences were insignificant or depended on the initial concentrations. Nutrients, suspended solids and coexisting heavy metals had significant effects on heavy metal accumulation in sludge when the initial concentration was controlled.     

Impact of sewage sludge conditioning and dewatering on the fate of nonylphenol in sludge-amended soils

The fate of (14)C-labelled p353-nonylphenol (NP) in soils amended with differently treated sludges originating from the same precursor sludge was assessed. The effects of commonly applied conditioning and dewatering techniques were investigated. Nonylphenol was degraded considerably faster in soils amended with liquid sludge, while a significant portion of it remained intact and extractable by organic solvents when sludge had been centrifuged before soil amendment. Mineralization was reduced or even inhibited when freeze-thaw or lime conditioning was applied, respectively. Flocculation by an acrylamide-based cationic polymer led to the formation of a nitro-addition product of nonylphenol in soil, as well to decreased mineralization rates after prolonged incubation times. Possible mechanisms underlying the observations are suggested and discussed.     

Occurrence and behaviour of linear alkylbenzenesulphonates, nonylphenol, nonylphenol mono- and nonylphenol diethoxylates in sewage and sewage sludge treatment

The fluxes of linear alkylbenzenesulphonates (LAS), nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) through sewage and sludge treatment of 29 Swiss sewage treatment plants were investigated. Reversed-phase high-performance liquid chromatography (HPLC) was used to determine LAS. Normal-phase HPLC was employed to measure NP, NP1EO and NP2EO which are metabolites of the nonionic surfactants of the nonylphenol polyethoxylate type (NPnEO). Quantitative determinations were performed of raw sewage, primary and secondary effluents and of sewage sludge. Under normal conditions of sewage and sludge treatment, LAS were efficiently removed from the raw wastewater (> 99% w/w) and were partly transferred to the sewage sludge (15–20% w/w). About 50% (molar base) of NPnEO in the sewage were transformed to NP and accumulated in the digested sludge. Large variations existed among different sewage treatment plants. It was estimated that 1.0 g m⁻² y⁻¹ of LAS and 0.3 g m⁻² y⁻¹ of NP are applied with sewage sludge to Swiss soils.     

Occurrence and elimination of antibiotics at four sewage treatment plants in the Pearl River Delta (PRD), South China

In this paper, the occurrence and elimination of eight selected antibiotics mainly for human use, including chloramphenicol, fluoroquinolone, sulfonamide and macrolide groups, were investigated at four sewage treatment plants (STPs) in the Pearl River Delta (PRD), South China. The most frequently detected antibiotics in the present study were ofloxacin, norfloxacin, roxithromycin, erythromycin-H(2)O (the main degradation product of erythromycin) and sulfamethoxazole. The concentrations of these compounds in raw influents and final effluents at the four STPs ranged from 10 to 1978 ngL(-1) and from 9 to 2054 ngL(-1), respectively. The other analytes were detected only in a few samples from the four STPs. Antibiotics could not be eliminated completely at the four STPs, with the highest elimination efficiency reaching to 81%. Analysis of the dissolved daily mass flow showed that fluoroquinolones were mostly eliminated from the sewage, and high concentrations of these compounds were found in secondary sludge. Therefore, it can be concluded that the observed elimination of fluoroquinolones in the STPs was due to their sorption to the sludge, but not biodegradation. Macrolides, especially erythromycin-H(2)O, were stable in sewage during the treatment process, and in fact even higher concentrations were found in the final effluents than in the raw sewages. Sulfamethoxazole was also found in raw influent and final effluent, indicating that it could withstand different treatment processes in the STPs. Remarkable differences in the daily environmental loads (the sum of the amounts in the final effluent and sludge) of the five most frequently detected antibiotic compounds were found in the range of 0.5-828 g at the four STPs.     

Removal of metals and fate of N and P in the bacterial leaching of aerobically digested sewage sludge

The solubilization of metals from aerobically digested sewage sludge was performed biologically using Thiobacillus ferrooxidans, in a continuously stirred tank reactor (CSTR). Experiments involved the preacidification of the sludge to pH 4.0 and the addition of 4 g FeSO₄-7H₂O per liter of sludge. Reactors were operated with 20 g/l total solids (2% TS), 0.5 volume of air per reactor volume per minute, agitation at 300 rpm and a 20% recirculation rate. A minimal mean hydraulic residence time (t) of 0.75 day, one half the time required in a batch system, resulted in solubilization of 52% of the Cu, 62% of the Zn and 78% of the Mn. The leached sludge was more easily dewatered than untreated sludge, and would not likely require the addition of polymer if a plate filter press were used. Metals did not reprecipitate during filtration. A small quantity of added lime was sufficient to precipitate the metals; selective precipitation could permit the separation of ferric hydroxide from valuable metals (Cu, Zn, Ni, Cd), which may then be recovered. No significant changes in the total nitrogen and phosphorus content occurred during solubilization. Biological solubilization produced a better quality sludge for agriculture, as well as avoiding the dispersal of metals into the environment.     

Occurrence and risk assessment of nonylphenol and nonylphenol ethoxylates in sewage sludge from different conventional treatment processes

In the present work, the concentrations of the organic pollutants nonylphenol (NP) and nonylphenol mono- and diethoxylates (NP1EO and NP2EO, respectively) in primary, secondary, mixed, aerobically-digested, anaerobically-digested, dehydrated, compost and lagoon sludge samples from different sludge treatments have been evaluated. Toxicological risk assessment of these compounds in sludge and sludge-amended soil has also been reported. NP, NP1EO and NP2EO were monitored in sludge samples obtained from treatment plants located in Andalusia (south of Spain) based on anaerobic treatments (11 anaerobic-digestion wastewater treatment plants and 3 anaerobic wastewater stabilization ponds) or on aerobic treatments (3 aerobic-digestion wastewater treatment plants, 1 dehydration treatment plant and 2 composting plants). The sum of NP, NP1EO and NP2EO (NPE) concentrations has been evaluated in relation to the limit value of 50 mg/kg set by the European Union Sludge Directive draft published in April 2000 (Working Document on Sludge). In most of the samples, NP was present at higher concentration levels (mean value 88.0 mg/kg dm) than NP1EO (mean value 33.8 mg/kg dm) and NP2EO (mean value 14.0 mg/kg dm). The most contaminated samples were compost, anaerobically-digested sludge, lagoon sludge and aerobically-digested sludge samples, which contained NPE concentrations in the ranges 44-962 mg/kg dm, 8-669 mg/kg dm, 27-319 mg/kg dm and 61-282 mg/kg dm, respectively. Risk quotients, expressed as the ratios between environmental concentrations and the predicted no-effect concentrations, were higher than 1 for NP, NP1EO and NP2EO in the 99%, 92% and 36% of the studied samples, respectively; and higher than 1 in the 86%, 6% and 2%, respectively, after sludge application to soil, leading to a significant ecotoxicological risk mainly due to the presence of NP.     

Occurrence and removal of selected organic micropollutants at mechanical, chemical and advanced wastewater treatment plants in Norway

In Norway the combined hydraulic capacity of all domestic wastewater treatment plants is relatively equally distributed between three major treatment plant types; mechanical, chemical, and combined chemical and biological. The Western coast from Lindesnes in the south to the Russian boarder in the North is dominated by mechanical treatment plants, constituting approximately 68% of the treatment capacity in that area. In the present study we report concentrations and removal efficiencies of polycyclic aromatic hydrocarbons (PAHs), nonylphenols, phthalates, polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) found in five Norwegian wastewater treatment plants (WWTPs) applying different levels of treatment. Concentrations of organic micropollutants in the influents to the WWTPs were generally in the low range of what have been reported by others for domestic wastewater in Europe and North-America. More than 90% removal could be obtained for nonylphenols, PBDEs, and the more hydrophobic 4-6 ring PAHs by chemical precipitation, however, biological treatment appeared to be necessary for efficient removal of the less lipophilic 2 and 3 ring PAHs, the medium- to short-chained nonylphenol ethoxylates and diethyl phthalate. SigmaPCB(7) was removed by more than 90% by combined biological/chemical treatment, while removal efficiency by chemical treatment was not possible to estimate due to low inlet concentrations. Low or insignificant removals of PAHs, phthalates and nonylphenols with their ethoxylates were observed at the mechanical WWTP, which was in accordance with the minuscule removal of TOC.     

Polar pollutants in municipal wastewater and the water cycle: Occurrence and removal of benzotriazoles

1H-benzo-1,2,3-triazole (BTri) and its methylated analogues (tolyltriazole, TTri) are corrosion inhibitors used in many industrial applications, but also in households in dishwashing agents and in deicing fluids at airports and elsewhere. BTri and one of the TTri-isomers (4-TTri) are typical examples of polar and poorly degradable trace pollutants. Benzotriazole elimination in four wastewater treatment plants (WWTP) in Berlin ranged from 20 to 70% for 5-TTRi over 30 to 55% for BTri to insignificant for 4-TTri. WWTP effluent concentrations were in the range of 7-18 μg/L of BTri, 1-5 μg/L of 4-TTri and 0.8-1.2 μg/L of 5-TTri. BTri and 4-TTri proved to be omnipresent in surface waters of the rivers Rhine and Elbe with concentrations increasing from <0.05 μg/L to around 0.5 μg/L of BTri and 0.2-0.5 μg/L of 4-TTri over 600-700 km. Bank filtration is an important process to generate raw water for drinking water production from surface waters. Even after residence times of several months BTri and 4-TTri were determined in concentrations of a few hundred ng/L in bank filtration water. Isotherm data from batch experiments indicate that activated carbon filtration should be suitable to avoid intrusion of TTri into drinking water in partially closed water cycles. For BTri, however, sorption to activated carbon appears to be too weak and ozonation may be mandatory to remove it from raw waters.     

Occurrence and seasonal variations of Giardia in wastewater and river water from Al-Jinderiyah region in Latakia,Syria

ABSTRACT

This study investigates the occurrence and concentration of Giardia cysts in wastewater and river water samples in Al-Jinderiyah region, Latakia, Syria. A total of 120 samples were collected between October 2016 and October 2017 from influent and effluent of Al-Jinderiyah Waste Water Treatment Plant (WWTP) and from three contaminated river water sites. Samples were concentrated and subjected to microscopic examination. The results show that the concentrations of cysts ranged from 0 to 297 cysts/L in wastewater samples. The overall removal efficiency of cysts in the activated sludge WWTP was 84.35%. The concentrations of cysts ranged from 0 to 128.52 cysts/L in river water samples. The highest concentration in river water was recorded near the raw wastewater discharge point. Seasonal variations of Giardia cysts concentration were significant, and the highest concentrations were recorded in the rainy season. The results suggest that Giardia may pose a public health risk in the studied region.     

Microbiota in anaerobic digestion of sewage sludge with and without co‐substrates

In this study, seven full‐scale anaerobic digesters, with or without co‐substrate regime, were analysed by physicochemical and molecular biological methods. A combination of robust community fingerprinting and Illumina MiSeq sequencing revealed a core bacterial community dominated by Chloroflexi, Firmicutes, Bacteroidetes and Proteobacteria, with variations in the profiles because of differences in the co‐substrate feeding regime. Despite these differences, physicochemical properties revealed a stable performance of all reactors, indicating a resilient bacterial microbiota in all full‐scale reactors. A rich bacterial core community ensured reactor functionality, whilst feeding regime and reactor type impacted the overall and the core bacterial diversity. Within the Archaea, Methanosaeta dominated in all reactors. Results indicated no relationship between archaeal community structure and the type of co‐substrate digested. Methanogens rely on the metabolic end products of bacterial activity and are thus less dependent on differences in the initial co‐substrate regime.     

Occurrence and removal of estrogens and beta blockers by various processes in wastewater treatment plants

This study aims at evaluating occurrence and treatment efficiency of five estrogenic hormones and ten beta blockers in wastewater treatment plants (WWTP). The use of consistent sampling procedures, analytical techniques and data processing enabled to achieve an accurate comparison of the performances of the different treatment processes. First, the occurrence of molecules was evaluated in fourteen rural and urban WWTP located in France. Free and total estrogens were analyzed showing that more than 84% of estrogens in the dissolved phase of influent samples are in the free form. In effluent samples, comparable mean values but higher variation are underlined (RSD from 13 to 54% depending on the estrogen, compared to 11-21% for influents). Most of the target molecules are quantified in 30 influent and 31 effluent samples. Similar occurrence frequencies are obtained for influents from rural (6 WWTP) and urban areas (8 WWTP), except for betaxolol which is only quantified in urban wastewaters. Removal efficiencies of 8 biological treatments were studied: suspended growth biomass (activated sludge) and attached growth systems (biofilter, rotating biological contactor, reed-bed filter, trickling filter). Biological treatments are efficient to remove estrogens from the dissolved phase, with removal rate around 90%. For beta blockers, acebutolol and nadolol are efficiently removed (mean removal rate of 80%), whereas sotalol and propranolol are hardly impacted by biological treatments (removal rate below 20%). Finally, 9 tertiary treatment processes were evaluated. Ozonation, reverse osmosis and activated carbon filtration prove a high removal efficiency for beta blockers (above 80%). On the contrary, high speed chemical settler, sand filtration, silex filtration, microfiltration and UV present generally removal rates below 30% for all beta blockers. The polishing pond studied presents variable removal performances depending on the molecules (up to 75% for propranolol). The role of the hydraulic retention time on the removal efficiencies is confirmed.     

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

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