Secondary-treated Municipal Wastewater Research Articles

Sustainable bioelectric activation of periodate for highly efficient micropollutant abatement

The periodate (PI)-based advanced oxidation process is valued for environmental remediation, but current activation methods involve high costs, secondary contamination risks, and limited applicability due to external energy inputs (e.g., UV), catalyst incorporation (e.g., Fe2+), or environmental modifications (e.g., freezing). In this work, novel bioelectric activation of PI using the electrons generated by electroactive bacteria was developed and investigated for rapid removal of carbamazepine (CBZ), achieving 100 %, 100 %, and 76 % removal efficiency for 4.22 µM of CBZ in 20 min at pH 2, 120 min at pH 6.4, and HRT of 30 min at pH 8.5, respectively, with a 1 mM PI dose and without an input voltage. It was deduced that electrons derived from bacteria could directly activate PI using Ti mesh electrodes and generate •IO3 via single electron transfer under strongly acidic conditions (e.g., pH 2). Nevertheless, under weak alkaline conditions (e.g., pH 8.5), biogenic electrons indirectly activated PI by generating OH−via 4e−reduction at the Ti mesh cathode, resulting in the formation of •O2− and 1O2. In addition to the metal cathode, a carbon-based cathode finely modulates the 2e−reduction, yielding H2O2 and activating PI to mainly form •OH. Moreover, primarily non-toxic IO3− was produced during treatment, while no detectable reactive iodine species (HOI, I2, and I3−) were observed. Furthermore, the bioelectric activation of PI demonstrated its capability to remove various micropollutants present in secondary-treated municipal wastewater, showcasing its broad-spectrum degradation ability. This study introduces a novel, cost-effective, and environmentally friendly PI activation technique with promising applicability for micropollutant elimination in water treatment.

Fungi-assisted bio-flocculation of Picochlorum sp.: A novel bio-assisted treatment system for municipal wastewater

Integration of microalgal cultivation with wastewater reclamations are sustainable valorizations approach to nutrients removal and lipid-rich biomass production. Lower growth rates and higher harvesting costs are the major bottlenecks of algal-based wastewater treatment process. Therefore, this study was carried-out to investigate lipid-rich biomass production using wastewater and demonstrate the low-cost biomass harvesting method. Picochlorum sp. BDUG 100241 (PC) was explored in various combinations of untreated raw municipal wastewater (UTMWW) and secondary treated municipal wastewater (STMWW) with a conventional ASN-III medium. The day-night cycles, pH, and aeration were optimized to improve PC biomass production. For harvesting of PC biomass, different concentrations of filamentous fungi Aspergillus niger MTCC 281 (A. niger) and Stropharia sp. ITCC-8422 assisted bioflocculation approach was investigated. In the first phase of optimization, PC showed maximum nutrient removal efficiency and growth in 50 % STMWW +50 % ASN-III. The present results indicated that a 12:12 h day-night cycle and a pH of 7.0 with aeration resulted in the highest nutrient removal efficiency of COD (90.92 %), phosphate (92.26 %) and nitrate (87.20 %). This optimized conditions also improved the biomass production (2.66 g/L), lipid content (44.04 %), photosynthetic and carotenoids (astaxanthin and β-carotene) production. Further, 10 % Stropharia sp. and A. niger granulated pellets signified the bioharvesting of PC biomass with maximum bioflocculation efficiency of 90.15 % and 92.48 %, respectively. The incorporation of bioflocculants, namely Stropharia sp. and A. niger for the harvesting of microalga biomass facilitated the removal of nutrients, enhanced biomass production (4.21 and 4.01 g/L), and augmented lipid content (43.0 % and 47.33 %) respectively.

Ozonation using a stainless-steel membrane contactor: Gas-liquid mass transfer and pharmaceuticals removal from secondary-treated municipal wastewater

A tubular porous stainless steel membrane contactor was characterized in terms of ozone-water mass transport, as well as its application in removing 23 pharmaceuticals (PhACs) detected in the secondary-treated municipal wastewater, under continuous mode operation. The volumetric mass transfer coefficient (KLa) was evaluated based on liquid flow rate, gas flow rate, and ozone gas concentration. The KLa values were substantially improved with an increment in liquid flow rate (1.6 times from 30 to 70 dm3 h−1) and gas flow rate (3.6 times from 0.30 to 0.85 Ndm3 min−1) due to the improved mixing in the gas-liquid interface. For the lowest liquid flow rate (30 dm3 h−1), the water phase boundary layer (82%) exhibited the major ozone transfer resistance, but it became almost comparable with membrane resistance for the highest liquid flow rate (70 dm3 h−1). Additionally, the influence of the specific ozone dose (0.39, 0.53, and 0.69 g O3 g DOC−1) and ozone inlet gas concentration (CO3,g,in = 27, 80, and 134 g Nm−3) were investigated in the elimination of 23 PhACs found in secondary-treated municipal wastewater. An ozone dose of 0.69 g O3 g DOC−1 and residence time of 60 s resulted in the removal of 12 out of the 23 compounds over 80%, while 17 compounds were abated above 60%. The elimination of PhACs was strongly correlated with kinetic reaction constants values with ozone and hydroxyl radicals (kO3 and kHO•), leading to a characteristic elimination pattern for each group of contaminants. This study demonstrates the high potential of membrane contactors as an appealing alternative for ozone-driven wastewater treatment.

Enteric virus removal by municipal wastewater treatment to achieve requirements for potable reuse

Primary and secondary treatment of municipal wastewater contributes to virus removal upstream of advanced purification to produce water for potable reuse. In this study, virus occurrence by cultivable and molecular methods was measured over a 24-month period in raw wastewater influents and secondary effluents from two municipal wastewater treatment plants that together provide the recycled water source for an advanced water purification facility. Using a rank-paired, covariance-based statistical approach, virus log removal values were determined for four wastewater treatment processes that operate in parallel at the two facilities (two activated sludge processes, trickling filter process, and trickling filter/solids contactor process). The trickling filter process exhibited the lowest observed removal of cultivable enteric virus with a median removal of 1.0 log10 (or 90% removal) and a 5th percentile log removal of 0.73 (or 82%), compared to the greatest removal observed for one of the activated sludge processes (median log removal of 2.4 or 99.6% and 5th percentile of 2.1 or 99.2%). Median log removal observed for male-specific (MS) and somatic (SOM) coliphage was 1.8 (98.6% removal) and 0.5 (70%), respectively, for trickling filter and 2.9 (99.9%) and 2.0 (99%) for activated sludge. Thus, coliphage removal was fairly similar to removal observed for cultivable enteric virus. The cultivable enteric virus 5th percentile removal (0.7) from the trickling filter treatment process was proposed to the state regulator for credit towards state requirements for virus removal related to groundwater augmentation with purified recycled water. Receiving pathogen removal credits for secondary wastewater treatment would allow for an improved margin (safety factor) of credits beyond the minimum required; and in this case may also increase the number of viable future groundwater recharge sites closer to drinking water production wells by reducing the underground travel time otherwise required to obtain sufficient credits.

Investigating the effects of irrigation with indirectly recharged groundwater using recycled water on soil and crops in semi-arid areas

The utilization of direct wastewater for irrigation poses many environmental problems such as soil quality deterioration due to the accumulation of salts, heavy metals, micro-pollutants, and health risks due to undesirable microorganisms. This hampers its agricultural reuse in arid and semi-arid regions. To address these concerns, the present study introduces a recent approach that involves using indirectly recharged groundwater (GW) with secondary treated municipal wastewater (STW) for irrigation through a Soil Aquifer Treatment-based system (SAT). This method aims to mitigate freshwater scarcity in semi-arid regions. The study assessed GW levels, physicochemical properties, and microbial diversity of GW, and soil in both impacted (receiving recycled water) and non-impacted (not receiving recycled water) areas, before recycling (2015–2018) and after recycling (2019–2022) period of the project. The results indicated a significant increase of 68–70% in GW levels of the studied boreholes in the impacted areas. Additionally, the quality of indirectly recharged GW in the impacted areas improved notably in terms of electrical conductivity (EC), hardness, total dissolved solids (TDS), sodium adsorption ratio (SAR), along with certain cations and anions (hard water to soft water). No significant difference was observed in soil properties and microbial diversity of the impacted areas, except for EC and SAR, which were reduced by 50% and 39%, respectively, after the project commenced. The study also monitored specific microbial species, including total coliforms, Escherichia coli (as indicator organisms), Shigella, and Klebsiella in some of the harvested crops (beetroot, tomato, and spinach). However, none of the analysed crops exhibited the presence of the studied microorganisms. Overall, the study concludes that indirectly recharged GW using STW is a better sustainable and safe irrigation alternative compared to direct wastewater use or extracted hard GW from deep aquifers.

Microplastic emission trends in Turkish primary and secondary municipal wastewater treatment plant effluents discharged into the Sea of Marmara and Black Sea

Wastewater Treatment Plants (WWTPs) are recognized as one of the primary sources of microplastics, a class of contaminants that has lately gained attention. The quantity of MP that WWTPs release into the environment depends on several factors, including the treatment type, season, and population serviced. MP abundance and characterization were explored in 15 WWTP effluent waters, 9 discharged to the Black Sea from Türkiye and 6 to the Marmara Sea, with varying population densities and treatment methods. The mean MP abundance in primary treatment WWTPs (76.25 ± 49.20 MP L−1) was found to be substantially greater than that in secondary treatment WWTPs (20.57 ± 21.56 MP L−1) (p<0.05). MPs in WWTP effluent waters showed significant seasonal and spatial differences (Two Way ANOVA, Tukey, p<0.05). However, no positive correlation was detected between the population serviced and MP abundance in effluent waters. While the fiber was the dominant shape (49.5%) among MPs in effluent waters, ≈80% of the length was <1000 μm. MPs are classified into polymer types as follows: polyethylene terephthalate (34.9%) > polypropylene (32.4%) > polyethylene (19.9%) > polyamide (11%) > polystyrene (1.2%) > polyvinyl chloride (0.6%). With effluent waters from the WWTPs tested, we calculated that 1.24x1010 daily MPs are discharged into the Black Sea while 4.95x1010 MPs are into the Marmara Sea, for a combined annual discharge of 2.26x1013 MPs highlighting that WWTPs are key contributors of MP in Turkish coastal waters.

Water Availability and Status of Wastewater Treatment and Agriculture Reuse in China: A Review

Due to climate change, 2/3 of the world’s population will face water shortage problems by 2025, while a 50% increase in food production is required in 2050 to feed nine billion people. In addition, the intensified anthropogenic activities have significantly increased water resource pollution. In this condition, wastewater reuse for crop irrigation to reduce water scarcity is currently becoming global, while it often causes soil pollution and heavy metal accumulation in agricultural areas. This situation has increased public concern over its environmental impact. Thus, an integrated framework was conducted to discuss the status of water availability in China, wastewater treatment and reuse in irrigation systems, and the potential health risks. Avenues for new research toward sustainable agriculture were discussed. We emphasize that wastewater reuse reduces the freshwater deficit and increases food productivity. However, adequate treatment should be applied before use to reduce its adverse impacts on human health risks and environmental pollution. Facilities and policies should support more accessible access to reclaimed water used in industries and urban facilities from secondary municipal wastewater treatment plants. This could be a long-term solution to eradicate water scarcity and inefficient water resources in agricultural systems.

Assessing groundwater recharge rates, water quality changes, and agricultural impacts of large-scale water recycling

The over-exploitation and insufficient replenishment of groundwater (GW) have resulted in a pressing need to conserve freshwater and reuse of treated wastewater. To address this issue, the Government of Karnataka launched a large-scale recycling (440 million liters/day) scheme to indirectly recharge GW using secondary treated municipal wastewater (STW) in drought-prone areas of Kolar district in southern India. This recycling employs soil aquifer treatment (SAT) technology, which involves filling surface run-off tanks with STW that intentionally infiltrate and recharge aquifers. This study quantifies the impact of STW recycling on GW recharge rates, levels, and quality in the crystalline aquifers of peninsular India. The study area is characterized by hard rock aquifers with fractured gneiss, granites, schists, and highly fractured weathered rocks. The agricultural impacts of the improved GW table are also quantified by comparing areas receiving STW to those not receiving it, and changes before and after STW recycling were measured. The AMBHAS_1D model was used to estimate the recharge rates and showed a tenfold increase in daily recharge rates, resulting in a significant increase in the GW levels. The results indicate that the surface water in the rejuvenated tanks meets the country's stringent water discharge standards for STW. The GW levels of the studied boreholes increased by 58–73 %, and the GW quality improved significantly, turning hard water into soft water. Land use land cover studies confirmed an increase in the number of water bodies, trees, and cultivated land. The availability of GW significantly improved agricultural productivity (11–42 %), milk productivity (33 %), and fish productivity (341 %). The study's outcomes are expected to serve as a role model for the rest of Indian metro cities and demonstrate the potential of reusing STW to achieve a circular economy and a water-resilient system.

Effectiveness of pulse dosing of submicron super-fine powdered activated carbon in preventing transmembrane pressure rise in outside-in-type tubular and inside-out-type monolithic ceramic membrane microfiltrations

Membrane fouling is still a major problem in water treatment that uses membrane separation. In this study, submicron-sized super-fine powdered activated carbon (SSPAC) was applied in a pulse/continuous dose to ceramic-membrane microfiltrations of two very different types: a submerged tubular membrane system that enabled vacuum-driven, outside-in filtration and a monolithic membrane system that enabled pressure-driven, inside-out filtration. Constant-flux filtration with repeated hydraulic backwashing was performed using diluted secondary-treated municipal wastewater and natural river water, and the effect and mechanism of membrane fouling mitigation were investigated. Pulse dosing with SSPAC alleviated a rise of transmembrane pressure (TMP) more than continuous dosing in the submerged tubular membrane system because of the effects, inter alia, associated with precoating the SSPAC layer as well as adsorption, by which soluble membrane foulants were effectively removed. Moreover, pulse-dosed SSPAC combined with a coagulant formed a precoat layer on the membrane that was easy to peel off with hydraulic backwashing. Continuous dosing of SSPAC was inferior to pulse dosing of SSPAC in terms of water quality, and some SSPAC was left on the membrane surface after hydraulic backwashing. In the monolithic membrane system, however, the superiority of pulse dosing of SSPAC was not observed: pulse and continuous dosing of SSPAC led to similar reductions of TMP rise. The SSPAC layer was unevenly distributed along the length of a channel and between channels in the monolithic membrane.

Decision Making Model for Municipal Wastewater Conventional Secondary Treatment with Bayesian Networks

Technical, economic, regulatory, environmental, and social and political interests make the process of selecting an appropriate wastewater treatment technology complex. Although this problem has already been addressed from the dimensioning approach, our proposal in this research, a model of decision making for conventional secondary treatment of municipal wastewater through continuous-discrete, non-parametric Bayesian networks was developed. The most suitable network was structured in unit processes, independent of each other. Validation, with data in a mostly Mexican context, provided a positive predictive power of 83.5%, an excellent kappa (0.77 &gt; 0.75), and the criterion line was surpassed with the location of the model in a receiver operating characteristic (ROC) graph, so the model can be implemented in this region. The final configuration of the Bayesian network allows the methodology to be easily extended to other types of treatments, wastewater, and to other regions.

Non-target and suspect-screening analyses of hydroponic soybeans and passive samplers exposed to different watershed irrigation sources

Water scarcity increases the likelihood of irrigating food crops with municipal wastewater that may pose potential dietary risks of regulated and non-regulated organic chemical uptake to edible plant tissues. Only a few studies have used high resolution mass spectrometry (HRMS) to assess the uptake of chemicals of concern into food crops. This study used non-target and suspect-screening analyses to compare total chemical features, tentatively identified chemicals (TICs), and EPA ToxCast chemicals in soybean plants and passive samplers exposed to five different irrigation sources that were collected from an agricultural watershed during mild drought conditions. Secondary-treated municipal wastewater effluent, two surface waters, two ground waters, and deionized municipal tap water were used for two hydroponic experiments: soybean roots and shoots and Composite Integrative Passive Samplers (CIPS) harvested after fourteen days of exposure and soybeans after fifty-six days. CIPS were sealed in separate glass amber jars to evaluate their efficacy to mimic chemical features, TICs, and ToxCast chemical uptake in plant roots, shoots, and beans. Total soybean biomass and water use were greatest for tap water, municipal wastewater, and surface water downstream of the municipal wastewater facility relative to groundwater samples and surface water collected upstream of the wastewater facility. ToxCast chemicals were ubiquitous across watershed irrigation sources in abundance, chemical use category, and number. Wastewater-exposed soybeans had the fewest extractable TICs in plant tissues of all irrigation sources. More ToxCast chemicals were identified in CIPS than extracted from irrigation sources by solid phase extraction. ToxCast chemicals in beans and CIPS were similar in number, chemical use category, and log Kow range. CIPS appear to serve as a useful surrogate for ToxCast chemical uptake in beans, the edible food product.

Regeneration and modelling of a phosphorous removal and recovery hybrid ion exchange resin after long term operation with municipal wastewater

Adsorption represents one of the most promising process for phosphorous (P) removal and recovery from municipal wastewater, but questions about its long-term stability remain. The goals of this work were (i) to assess changes in morphology and adsorption performances of hybrid anion exchanger (HAIX) LayneRT after 2.5 years of operation in a 10 m3 d−1 demonstration plant fed with secondary-treated municipal wastewater, (ii) to optimize the LayneRT regeneration procedure, and (iii) to evaluate the suitability of the ion exchange model to describe P adsorption on LayneRT. LayneRT is composed of hydrated ferric nanoparticles dispersed in a strong base anion exchange resin. Batch and continuous flow adsorption/desorption tests were conducted with the resin used for 2.5 years, regenerated with two alternative solutions: NaOH, reactivating mainly the iron nanoparticles active sites, and NaOH + NaCl, also regenerating the active sites of the ion exchange media. The physicochemical characterization by Scanning Electron Microscope indicated that regeneration by NaOH significantly reduced the deterioration of the resin surface, even after 59 adsorption/desorption cycles. Lab-scale continuous flow tests showed that the resin regenerated with either solution featured P adsorption performances very close to that of the virgin resin. The isotherm tests showed that P adsorption by LayneRT was effectively simulated with the ion exchange model. This study confirms that LayneRT is a durable, resistant and promising media for P recovery from wastewater.

Prediction of Peracetic Acid Disinfection Performance for Secondary Municipal Wastewater Treatment Using Artificial Neural Networks

Disinfection is one of the most critical processes for municipal wastewater treatment. However, traditional chemical dosing approaches do not consider how changes in water quality and process opera...

The Effect of Secondary-Treated Municipal Wastewater Discharge on Nutrient Concentrations in Leaves and Soils of Gray Mangrove in Bahrain

The wastewater discharge into the marine environment may affect the integrity of the mangrove ecosystem. In this context, the possible effect of secondary-treated municipal wastewater discharge on the nutrient concentrations in the leaves and soils of Tubli Bay gray mangrove (Avicennia marina (Forsk.) Vierh.) was assessed at three sites. Physical properties and the percent of organic matter content in mangrove soil were measured. The nitrogen concentration was measured using the Kjeldahl method. Extractable phosphorus was quantified using the dry-ash method. Plant and soil concentration of K, Ca, Mg, and Na was determined using an inductively coupled plasma analyzer. Soil organic matter was estimated using the dry-ash method. The results showed no significant differences in the mangrove leaves’ nutrient concentration between sites regarding all the measured variables except N and Na. Wastewater discharge significantly affects mangrove leaves N content at the Tubli site where heavy wastewater loads are discharged. Leaf nutrients’ concentration followed the order: Na&gt; K&gt; N&gt; Mg&gt; Ca&gt; P. Nutrients were concentrated in the topsoil layers in the following order: Ca &gt; Mg &gt; Na &gt; K &gt; N &gt; P. Nutrient level showed a decreasing pattern with soil depth, except for Ca. Significant differences were observed in N and P’s levels in the soil layers between the affected site and the other two sites. Furthermore, the soil analysis indicated significant differences in N and P levels in the Tubli site soil compared to the other two sites due to wastewater discharge. No significant correlations were found between nutrient levels in the leaves of mangrove and its underlying soils. Additionally, the release of wastewater into the Bay significantly increased soil organic matter in the affected site. The study’s findings indicate that the continued release of the secondary effluent into the Tubli Bay may alter the Bay ecosystem’s Physico-chemical properties in general and mangrove survival in particular.

Inhibition effect of dissolved organic matter in secondary-treated municipal wastewater on corrosion of N80 carbon steel

Abstract Secondary-treated municipal wastewater (MWW) is the alternative water source in recirculating cooling water systems. Municipal wastewater treatment plant (WWTP) effluent was collected and four fractions including hydrophobic acidic (HPOA), hydrophobic alkaline (HPOB), weakly hydrophobic (WHPO) and hydrophilic (HPI) organics were isolated from the effluent by using DAX-8/XAD-4 resin. We used potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) to investigate corrosion characteristics of N80 carbon steel in the different water samples and control samples. In contrast with control samples, the corrosion rate of N80 carbon steel decreased 41%, 23%, 18% and 4% in the presence of HPOA, HPOB, WHPO and HPI, respectively. The results were further confirmed by the EIS test. In the presence of the four fractions (especially HPOA), the radius of the semicircle in the Nyquist plot was much larger than that for the control samples, which indicated that the impedance in the EIS test of the HPOA sample was much higher than that of the control sample. The dissolved organic matter (DOM) could adsorb onto the surface of the electrode and form a protective film, which could inhibit electron transfer and increase the electrochemical impedance of the electrochemical test system.

Suitability of chlorine dioxide as a tertiary treatment for municipal wastewater and use of reclaimed water for overhead irrigation of baby lettuce

Reclaimed wastewater used for agricultural irrigation should meet specific microbiological standards in order to prevent microbial contamination of the irrigated produce. The objective of this study was to evaluate the suitability of chlorine dioxide (ClO2) for the disinfection of secondary-treated municipal wastewater and its subsequent use for overhead irrigation in greenhouse production of baby lettuce. The impact of reclaimed water tertiary-treated with ClO2 on E. coli concentration, the presence of pathogenic bacteria, and the occurrence of chlorates as disinfection by-products was evaluated in water and in baby lettuce. E. coli was quantified using both conventional plating methods and a quantitative real time PCR (qPCR) method with propidium monoazide (PMA) pre-treatment to differentiate between viable and non-viable bacteria. Population density of cultivable E. coli was significantly lower (p < 0.05) in reclaimed water, tertiary-treated using ClO2 (ClO2W), when compared with secondary-treated municipal wastewater (SW). However, no significant differences in viable but non-cultivable (VBNC) E. coli loads were observed between treatments when quantifying using the PMA-qPCR method. These results could indicate that ClO2 treatment of water did not kill the bacteria but it induced bacteria to enter a VBNC state. The proportion of samples positive for the presence of pathogenic bacteria was lower in ClO2W (1/8) compared with SW (7/8). Significantly lower E. coli counts (p < 0.05) were detected in plants irrigated with ClO2W compared with those irrigated with SW. Relationship between higher E. coli counts and the presence of pathogens was observed when lettuce samples were analyzed by PMA-qPCR (Mann-Whitney U Test, p < 0.05). Baby lettuce irrigated with ClO2W showed a significantly higher concentration of chlorates than lettuce irrigated with SW. The quantification of viable bacteria using molecular methods suggests that the efficacy of ClO2 could be overestimated when conventional plating quantification methods are used. Additionally, the accumulation of chlorates in the tissue should be considered as it represents an adverse effect of this disinfection treatment.

Micropollutants removal in tertiary moving bed biofilm reactors (MBBRs): Contribution of the biofilm and suspended biomass

The performance of tertiary moving bed biofilm reactors (MBBRs) was evaluated in terms of micropollutants (MPs) removal from secondary-treated municipal wastewater. After stepwise establishment of a mature biofilm, monitored by scanning electron and confocal microscopies, abiotic and biotic removals of MPs were deeply studied. Since no MPs reduction was observed by the both photodegradation and volatilization, abiotic removal of MPs was ascribed to the sorption onto the biomass. Target MPs i.e. Naproxen, Diclofenac, 17β-Estradiol and 4n-Nonylphenol, arranged in the ascending order of hydrophobicity, abiotically declined up to 2.8%, 4%, 9.5% and 15%, respectively. MPs sorption onto the suspended biomass was found around two times more than the biofilm, in line with MPs' higher sorption kinetic constants (ksor) found for the suspended biomass. When comparing abiotic and biotic aspects, we found that biotic removal outperformed its counterpart for all compounds as Diclofenac, Naproxen, 17β-Estradiol and 4n-Nonylphenol were biodegraded by 72.8, 80.6, 84.7 and 84.4%, respectively. The effect of the changes in organic loading rates (OLRs) was investigated on the pseudo-first order degradation constants (kbiol), revealing the dominant biodegradation mechanism of co-metabolism for the removal of Diclofenac, Naproxen, and 4n-Nonylphenol, while 17β-Estradiol obeyed the biodegradation mechanism of competitive inhibition. Biotic removals and kbiol values of all MPs were also seen higher in the biofilm as compared to the suspended biomass. To draw a conclusion, a quite high removal of recalcitrant MPs is achievable in tertiary MBBRs, making them a promising technology that supports both pathways of co-metabolism and competitive inhibition, next to the abiotic attenuation of MPs.

Mixed culture polyhydroxyalkanoate (PHA) synthesis from nutrient rich wet oxidation liquors

Organic waste residues can be hydrothermally treated to produce organic acid rich liquors. These hydrothermal liquors are a potential feedstock for polyhydroxyalkanoate (PHA) production. We investigated the effect of dissolved oxygen concentration and substrate feeding regimes on PHA accumulation and yield using two hydrothermal liquors derived from a mixture of primary and secondary municipal wastewater treatment sludge and food waste. The enriched culture accumulated a maximum of 41% PHA of cell dry weight within 7 h; which is among the highest reported for N and P rich hydrothermal liquors. Recovered PHA was 77% polyhydroxybutyrate and 23% polyhydroxyvalerate by mass. The families Rhodocyclaceae (84%) and Saprospiraceae (20.5%) were the dominant Proteobacteria (73%) in the enriched culture. The third most abundant bacterial genus, Bdellovibrio, includes species of known predators of PHA producers which may lead to suboptimal PHA accumulation. The PHA yield was directly proportional to DO concentration for ammonia stripped liquor (ASL) and inversely proportional to DO concentration for low strength liquor (LSL). The highest yield of 0.50 Cmol PHA/Cmol substrate was obtained for ASL at 25% DO saturation. A progressively increasing substrate feeding regime resulted in increased PHA yields. These findings demonstrate that substrate feeding regime and oxygen concentration can be used to control the PHA yield and accumulation rate thereby enhancing PHA production viability from nutrient rich biomass streams.

Micropollutants removal from secondary-treated municipal wastewater using weak polyelectrolyte multilayer based nanofiltration membranes

Nanofiltration (NF) is seen as a very promising technology to remove micropollutants (MPs) from wastewater. Unfortunately this process tends to produce a highly saline concentrate stream, as commercial NF membranes retain both the MPs and most of the ions. The high salinity makes subsequent degradation of the MPs in a bio-reactor very difficult. The main goal of this study is to prepare and study a NF membrane that combines a low salt rejection with a high MPs rejection for the treatment of secondary-treated municipal wastewater. This membrane was prepared using layer by layer (LbL) deposition of the weak polycation poly(allylamine hydrochloride) (PAH), and the weak polyanion poly(acrylic acid) (PAA), on the surface of a hollow fiber dense ultrafiltration (UF) membrane. The ionic strength of the coating solutions was varied and properties of the formed polyelectrolyte multilayers (PEMs), such as hydration, hydrophilicity, hydraulic resistance and ions retention were studied. Subsequently we tested the apparent and steady state rejection of MPs from synthetic wastewater under cross-flow conditions. The synthetic wastewater contained the MPs Diclofenac, Naproxen, Ibuprofen and 4n-Nonylphenol, all under relevant concentrations (0.5–40µg/L, depending on the MP). PEMs prepared at lower ionic strength showed a lower hydration and consequently a better retention of MPs than PEMs prepared at higher ionic strengths. A strong relationship between the apparent rejection of MPs and their hydrophobicity was observed, likely due to adsorption of the more hydrophobic MPs to the membrane surface. Once saturated (steady state), the molecular size of the MPs showed the best correlation with their rejection, indicating rejection on the basis of size exclusion. In contrast to available commercial NF membranes with both high salt and MP rejection, we have prepared an unique membrane with a very low NaCl retention (around 17%) combined with a very promising removal of MPs, with Diclofenac, Naproxen, Ibuprofen and 4n-Nonylphenol being removed up to 77%, 56%, 44% and 70% respectively. This membrane would allow the treatment of secondary treated municipal wastewater, strongly reducing the load of MPs, without producing a highly saline concentrate stream.

The effect of advanced secondary municipal wastewater treatment on the molecular composition of dissolved organic matter

There is a growing interest in water reuse and in recovery of nutrients from wastewater. Because many advanced treatment processes are designed to remove organic matter, a better understanding of the composition of dissolved organic matter (DOM) in wastewater is needed. To that end, we assessed DOM in the Nine Springs Wastewater Treatment Plant in Madison, Wisconsin by UV–visible spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Samples were collected from the influent and effluent of two different secondary treatment processes and their respective secondary clarifiers, the UV disinfection unit, and an Ostara treatment system, which produces struvite via chemical precipitation. The optical properties reveal that DOM throughout the plant is relatively aliphatic and is low in molecular weight compared to DOM in freshwater systems. Furthermore, the DOM is rich in heteroatoms (e.g., N, S, P, and Cl) and its molecular formulas are present in the lipid-, protein-, carbohydrate-, and lignin-like regions of van Krevelen diagrams. Secondary treatment produces DOM that is more aromatic and more complex, as shown by the loss of highly saturated formulas and the increase in the number of CHO, CHON, and CHOP formulas. The two secondary treatment processes produce DOM with distinct molecular compositions, while the secondary clarifiers and UV disinfection unit result in minimal changes in DOM composition. The Ostara process decreases the molecular weight of DOM, but does not otherwise alter its composition. The optical properties agree with trends in the molecular composition of DOM within the main treatment train of the Nine Springs plant.