Secondary Wastewater Treatment Research Articles

The new German standard on constructed wetland systems for treatment of domestic and municipal wastewater.

The German Association for Water, Wastewater and Waste e.V. (DWA) has published a new standard for the dimensioning, construction, and operation of constructed wetlands for treatment of domestic and municipal wastewater. The changes to the standard are based on a wide range of experience gained in recent years in Germany and Europe. For the first time ever, the standard has been officially translated and published in English. This paper summarizes the new standard for secondary treatment of domestic wastewater with classical one-stage unsaturated vertical flow (VF) wetlands, VF wetlands with lava sand for treatment of wastewater from combined sewer systems, and actively aerated VF and horizontal flow (HF) flow wetlands. Two-stage unsaturated VF wetlands treating raw wastewater (French VF wetlands), are also included in the new standard. HF wetlands are no longer described in the standard for secondary treatment of domestic wastewater. This does not exclude their application. Existing HF wetland systems in Germany may continue to be operated so long as effluent parameters are met and proper operations and maintenance is ensured. This paper gives an overview of the new design standard, including key information on wastewater type and loading, as well as primary attributes of each wetland design.

Strategic Approach for Prioritising Local and Regional Sanitation Interventions for Reducing Global Antibiotic Resistance

Globally increasing antibiotic resistance (AR) will only be reversed through a suite of multidisciplinary actions (One Health), including more prudent antibiotic use and improved sanitation on international scales. Relative to sanitation, advanced technologies exist that reduce AR in waste releases, but such technologies are expensive, and a strategic approach is needed to prioritize more affordable mitigation options, especially for Low- and Middle-Income Countries (LMICs). Such an approach is proposed here, which overlays the incremental cost of different sanitation options and their relative benefit in reducing AR, ultimately suggesting the “next-most-economic” options for different locations. When considering AR gene fate versus intervention costs, reducing open defecation (OD) and increasing decentralized secondary wastewater treatment, with condominial sewers, will probably have the greatest impact on reducing AR, for the least expense. However, the best option for a given country depends on the existing sewerage infrastructure. Using Southeast Asia as a case study and World Bank/WHO/UNICEF data, the approach suggests that Cambodia and East Timor should target reducing OD as a national priority. In contrast, increasing decentralized secondary treatment is well suited to Thailand, Vietnam and rural Malaysia. Our approach provides a science-informed starting point for decision-makers, for prioritising AR mitigation interventions; an approach that will evolve and refine as more data become available.

Assessment of drugs of abuse in a wastewater treatment plant with parallel secondary wastewater treatment train

In this study, 24-hour composite wastewater samples were collected from a wastewater treatment plant of New Zealand with parallel secondary treatment units. The aim was to investigate the occurrence, removal, and consumption of 13 drugs of abuse (DOAs) including illicit drugs, alcohol, nicotine, and their metabolites. The filtered samples were analysed through direct injection on LC-MS/MS. Ethyl sulfate, one of the major metabolites of alcohol, was detected at the highest concentration (mean = 8300 ng/L) in wastewater influent. The mean concentrations of methamphetamine and hydroxycotinine in the influent were found to be 935 ng/L and 5000 ng/L, respectively. Amphetamine (383 ng/L) and cocaine (286 ng/L) were detected at the highest concentrations in the effluent. The removal efficiency of the treatment plant varied for DOAs: >99% for morphine, ethyl sulfate, and hydroxycotinine and <50% for methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Primary treatment did not show any significant removal of DOAs while the removal efficiencies of total monitored DOAs by Membrane Bioreactor (MBR) and Bardenpho processes were found to be similar (~95% removal). The population was estimated using hydrochemical parameters and human urine biomarkers and showed good agreement with wastewater treatment plant's estimates. Weekday-weekend variation in the consumption of alcohol and methamphetamine was found to be significant, with a higher estimated consumption during the weekends. Monitored DOAs in influent were present at highest concentrations during summer (23 μg/L), at low concentrations during winter (17 μg/L), and at lowest concentrations during heavy rainfall event (11 μg/L), possibly due to dilution. The population normalised mass loads of DOAs were found to correlate with their metabolites, and morphine was found to correlate with nicotine metabolites.

Variability of release rate of flame retardants in wastewater treatment plants

Information on variability is important in the assessment of the releases and potential risks of brominated flame retardants (BRFs) in the environment, but related data are limited. In this study, two release-characterizing parameters, release fraction to final effluent and influent-biosolids transfer coefficient, were used to quantify releases of five BFRs from eight secondary wastewater treatment plants (WWTPs). The five BFRs are recalcitrant, hydrophobic, and low in volatility. The two parameters for these BFRs were found to vary from day to day and season to season within individual WWTPs as well as from one WWTP to another. These temporal and spatial variations were, however, comparable to each other and both within a factor of 3 above or below the parameter averages. Averages for release fraction were in the range of 0.02–0.29 and those for influent-biosolids transfer coefficient in the range of 3–26 L/g, depending upon a given BFR at a given WWTP. These ranges and the observed factor-3 variability are not only useful for estimating releases of the five BFRs, but more importantly provide read-across data for the assessment of substances with similar physical-chemical properties.

Effect of wastewater on properties of concrete

Water is one of nature's precious gifts to humanity. It was the most common liquid with the highest usage of all liquids on the globe. This elixir of lives is a restricted natural resource. Hence, even a drop should not be wasted and now it's time for its systematic use. Construction industry requires a lot of water for infrastructure. Therefore, use of treated wastewater in construction industries is gaining grounds in so many countries of the world. The proper selection and processing of treated wastewater may be helpful in manufacturing concrete. This research aim was to find the possibility of the usage of treated wastewater in concrete as an alternative to potable water by conducting comprehensive laboratory investigations for a better understanding of mechanical and durability properties of treated wastewater concrete. The samples of water used were tertiary treated wastewater (TTWW), secondary treated wastewater (STWW) and tap water (TW). Compressive strength test, flexural strength test, chloride penetration resistance, carbonation resistance and abrasion resistance test were carried out for each concrete mixes. Tap water was replaced with treated wastewater to 100% by weight. In this study water to cement ratio was taken as 0.47. For compressive strength, concrete cubes for 7, 28 and 90 days were cast and for flexural strength beams were cast for 28 and 90 days as well as durability test was carried out after the 28 days. The results of compressive strength of concrete after replacement of 100% tap water with tertiary treated wastewater in concrete mixing as well as curing in tap water and tertiary wastewater is found to be in the range of 85–94% of normal concrete, which satisfies ASTM C-94 norms. The flexural strength of tertiary treated wastewater with tap water curing and tertiary treated wastewater with TTWW curing shows significant results as compared to control concrete. The depth of carbonation observed lower in control concrete as compare to all mixes. The experimental results indicated that the chloride concentration of concrete samples increased with a decrease in the quality of mixing water.

Municipal wastewater treatment costs with an emphasis on assimilation wetlands in the Louisiana coastal zone

In recent decades, water quality standards for wastewater treatment have become more stringent, increasing costs and energy required to reduce pollutants. Wetland assimilation is a low-cost and low-energy alternative to traditional tertiary wastewater treatment where secondarily treated and disinfected municipal effluent is discharged primarily into freshwater forested wetlands in coastal Louisiana. In this paper, costs per gallon of treatment capacity for conventional secondary and tertiary treatment were compared to those for assimilation wetlands. Cost analysis reports were used to determine costs per gallon of treatment capacity for conventional wastewater treatment facilities, including costs for conveyance between the collection system and the assimilation wetland site, and between the treatment and disposal sites if they could not be co-located. Capital and operation and maintenance costs were considered. Because all wastewater treatment plants are required to treat at least to secondary standards, costs for primary and secondary treatment were combined. If necessary, these costs were adjusted for inflation to 2017 dollars using an average inflation rate of 2.19 percent and a cumulative inflation rate of 50.84 percent. To determine costs per gallon of treatment capacity for assimilation wetlands, actual costs provided by the project engineer were used when available. To simulate the future costs of facility construction and compare the replacement costs of conventional secondary and tertiary wastewater treatment facilities and treatment wetlands in the context of energy prices, U.S. Bureau of Labor and Statistics (BLS) data for the price index for inputs to construction were used, as were the Energy Information Administration (EIA) data for the price of crude oil to model future wastewater treatment plant construction and operation costs. The cost for the Mandeville assimilation wetland included $1 million for the price of the land. Future costs of treatment facility construction and operation were modeled relative to average price of construction inputs between 1998 and 2015 using the projected price of crude oil. When treatment costs were compared among secondary, tertiary, and assimilation wetlands, mean cost for assimilation wetlands was $0.60 per gallon (>1 MGD capacity) compared to $4.90 and $6.50 per gallon for secondary and tertiary treatment, respectively. The lower total costs and energy requirements for assimilation wetlands result in lower variability in the price of construction and operation. Wetland assimilation is more economical than conventional wastewater treatment, especially compared to advanced secondary and tertiary treatment. It is likely that energy costs will increase significantly in coming decades. Because conventional secondary and tertiary treatment are energy intensive, increases in energy costs will significantly increase the costs of these treatment systems. Treatment systems that combine lower technology (e.g., oxidation ponds) secondary treatment with wetland assimilation are less likely to be impacted by rising energy costs than traditional wastewater treatment.

Solar photo-Fenton oxidation for the removal of ampicillin, total cultivable and resistant E. coli and ecotoxicity from secondary-treated wastewater effluents

Urban, hospital and pharmaceutical industry wastewater effluents are among the main sources of antibiotics’ and other antimicrobial agents’ contamination in soil and water ecosystems, especially in countries where wastewater reuse is applied. Ampicillin (AMP), which is the first semi-synthetic broad spectrum penicillin that was released on the market in 1961 has been detected in treated wastewater effluents worldwide, at concentrations ranging from sub-ng/L up to 27 μg/L, as well as in various environmental aqueous matrices up to 13.7 μg/L, highlighting its recalcitrance to conventional biological treatment. Nevertheless, the degradation potential of AMP via advanced chemical oxidation processes, which are widely considered as promising alternatives of conventional technologies, hardly has been investigated. Thus, this study aims at assessing the efficiency of solar photo-Fenton process at degrading AMP from secondary-treated wastewater effluents under various experimental conditions. The degradation rate of AMP via solar photo-Fenton oxidation fitted well the pseudo-first-order kinetic model. AMP was completely degraded after 30 min of treatment at various H2O2 doses (25–100 mg/L) under acidic pH, while its degradation was pronounced at mild alkaline conditions (inherent pH) (100% removal after 5 min). Total cultivable and AMP-resistant E. coli was completely inactivated after 180 min of treatment at the optimum operational conditions, and no regrowth was observed. Finally, the ecotoxicity results showed that the process was capable of eliminating the toxicity towards Daphnia magna after 180 min, providing thus a more complete evaluation of the overall efficiency of the process.

The Use of Coagulation-UV Irradiation/H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; and Electrocoagulation Methods on Pulp and Paper Mill Wastewater Treatment

Effluents from pulp and paper mill typically consist of high loading of inorganics compounds (e.g., Na2CO3, Na2S, NaOH and NaCl) and organics compounds (e.g., lignin and polysaccharides fragments, alcohols, carboxylic acids) Several methods, such as biological, physical and chemical treatment, have been reported to degrade these molecules. However, coagulation is by far the cheapest, simplest and most common method employed for secondary wastewater treatment to reduce colour and organics. In this research, two most widely used methods were employed to treat a model wastewater of pulp and paper industry, namely a combination of coagulation-flocculation-UV irradiation/H2O2 and electrocoagulation (EC). In the application of coagulation-flocculation-UV irradiation/H2O2 method, the decrease in colour (measured as absorbance at 500 nm) was 71%, and the COD removal was measured to be 38% under the optimum conditions of pH 8, coagulant dose of 700 ppm, flocculant dose of 60 ppm, 130 rpm of coagulant stirring rate, 1 day irradiation time, and 25 mM of H2O2. For the EC method, 91% reduction of color and 84% reduction of COD were achieved at 40 min of electrolysis time, pH of 8, 600 ppm of NaCl concentration, electrode distance of 1.5 cm and 2 V of voltage. The EC method may serve as an efficient method for color and organics removals from pulp and paper mill wastewater.

Characterization of primary and secondary wastewater treatment sludge from a pulp and board mill complex to evaluate the feasibility of utilization as a soil amendment agent and a fertilizer product

In this study, we have determined the main important physical and chemical properties as well as the heavy metal concentrations of the primary and secondary wastewater treatment sludge from a pulp and board mill complex located in Finland in order to evaluate the utilization of these by-products as a soil amendment agent or a fertilizer product. Easily soluble Ca, Mg, K, Na, P and S concentrations in the sludges were extracted by ammonium acetate (CH 3 COONH 4 ) and easily soluble Cu, Mn and Zn concentrations by CH 3 COONH 4 + Na 2 EDTA. For the determination of total nutrient and total heavy metal concentrations in sludges, they were digested using aqua regia (3 mL HCl + 9 mL HNO 3 ). The total heavy concentrations in the primary sludge were lower than the Finnish heavy metal limit values for fertilizer products. In the secondary sludge, all other total heavy metals than the total Cd concentration (4.8 mg/kg; d.w.) were lower than the heavy metal limit values for fertilizer products. Due to the low total heavy metal concentrations, which were lower than the Finnish limit values for fertilizer products, the primary sludge is a potential fertilizer. Although the total Cd concentration (4.8 mg/kg; d.w.) in the secondary sludge exceed the limit value of 1.5 mg/kg (d.w.) for fertilizer products, this residue may be used as a soil improver, a growing media or as a fertilizer product in landfill sites or in other closed industrial areas, because the Finnish limit values for fertilizer products are not applied at these sites.

Micropollutant rejection of annealed polyelectrolyte multilayer based nanofiltration membranes for treatment of conventionally-treated municipal wastewater

The ever-increasing concentrations of micropollutants (MPs) found at the outlet of conventional wastewater treatments plants, is a serious environmental concern. Polyelectrolyte multilayer (PEM)-based nanofiltration (NF) membranes are seen as an attractive approach for MPs removal from wastewater effluents. In this work, PEMs of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were coated in a layer by layer (LbL) fashion on the surface of a polyacrylonitrile ultrafiltration support to obtain PEM-based NF membranes. The impact of PEM post-treatment, by applying salt and thermal annealing, was then investigated in terms of swelling, hydrophilicity, permeability, and ion rejection. While thermal annealing produced a more compact structure of PEM, it did not improve the ion rejection. Among the different salt concentrations examined for the salt-annealing process, the highest ion rejection was observed for (PAH/PAA)15 membranes annealed in 100 mM NaNO3, interestingly without any decrease in the water permeability. This membrane was studied for the rejection of four MPs including Diclofenac, Naproxen, 4n-Nonylphenol and Ibuprofen from synthetic secondary-treated wastewater, over a filtration time of 54 h. At an early stage of filtration, the membrane became more hydrophobic and a good correlation was found between the compounds hydrophobicity and their rejection. As the filtration continued until the membrane saturation, an increase in membranes hydrophilicity was observed. Hence, in the latter stage of filtration, the role of hydrophobic interactions faded-off and the role of molecular and spatial dimensions emerged instead in MPs rejection. To test the suitability of the membranes for the ease of cleaning and repeated use, the sacrificial PEMs and foulants were completely removed, followed by re-coating of PEMs on the cleaned membrane. The higher MPs rejection observed in salt-annealed membranes compared to the non-annealed counterparts (52–82% against 43–69%), accompanied with still low ion rejection, confirm the high potential of PEM post-treatment to achieve better performing PEM-based NF membranes.

Effects of irrigation with secondary treated wastewater on physicochemical and microbial properties of soil and produce safety in a semi-arid area

Water scarcity is becoming one of the largest problems worldwide. Agricultural reuse of wastewater has been considered a valuable and reliable alternative, alleviating the pressure on freshwater resources in arid and semi-arid regions such as the Middle East. Inadequate microbial quality of treated wastewater is a challenge for developing countries, which limits agricultural reuse of wastewater. This study assessed the impact of irrigation with secondary treated wastewater (STWW) on soil properties as well as the safety of various types of crops as compared with tap water (TW) irrigation through a furrow system. Total and fecal coliforms and Escherichia coli were monitored as indicator bacteria in STWW, irrigated soil and harvested crops. The presence of pathogenic E. coli O157, Salmonella and Shigella was also monitored in all samples using a combination of culture and molecular methods. The microbial quality of wastewater in terms of E. coli concentration (4.18 Log MPN/100 ml) failed to meet the world health organization (WHO) recommendation for irrigation of root and leafy crops (≤103 and ≤ 104E. coli per 100 ml for root and leafy crops, respectively). No significant effects on physicochemical properties of the soil irrigated with STWW was found in comparison with control plots, except for electrical conductivity (EC) and sodium adsorption ratio (SAR), which were slightly higher in STWW soil samples. Although the microbial quality of soil was affected by STWW irrigation, a relatively low concentration of E. coli was detected in soil. No microbial contamination in terms of E. coli was found on harvested maize and onion. E. coli contamination of lettuce and spring onion was found for both irrigation schemes. No STWW, soil or crop samples were found positive for pathogenic bacteria. According to the analyzed parameters, STWW could be safely used as an alternative source for irrigation of root and leafy crops.

Trends in organic micropollutants removal in secondary treatment of sewage

Organic micropollutants (OMPs) comprise a wide group of substances highly consumed in modern societies. There has been a growing social and scientific interest on OMPs in wastewaters in the twentyfirst century. This research paper has identified the evolution of the research trends in the period 2001–2017 on OMPs fate during secondary wastewater treatment. These trends have moved from a global perspective on the occurrence of OMPs in wastewaters to more specific research focussed on understanding their behaviour during advanced treatment processes. Based on a bibliometric analysis carried out using one of the leading scientific databases, pharmaceuticals have been identified as the main group of OMPs. An increasing number of publications have been released on the fate of pharmaceuticals in wastewater with a growing number of countries involved: from 38 publications belonging to 14 countries in first 5-year period analysed (2001–2005) up to 138 from 42 countries only in the last 2 years (2016–2017). The main operational conditions in wastewater treatment plants influencing the removal of OMPs, as well as the mechanisms involved depending on the physico-chemical characteristics of the substances are reviewed. The paper also considers the role of microbial populations, as well as technological and operational features in OMPs abatement. Finally, a specific section is dedicated to the metabolic and cometabolic biotransformations of some OMPs taking place under heterotrophic, nitrifying and anaerobic conditions, a more novel research trend explored more recently.

Formation and prevention of biofilm and mineral precipitate clogging in drip irrigation systems applying treated wastewater

Pressure-irrigation systems and, in particular, micro-irrigation provide an effective methodology for increasing irrigation efficiency. However, emitter clogging is a major problem in micro-irrigation systems, especially under irrigation with treated wastewater (TWW). Currently, farmers treat their irrigation system by periodical application of solutions of chemicals or washing the lateral lines. The aim of this study was to characterize treatments for the prevention of clogging in drip irrigation systems utilizing different qualities of TWW (secondary and tertiary TWW). A model system was designed and assembled to compare the flow rate (FR), fouling accumulation and fouling composition in laterals and drippers subjected to different treatments. Under irrigation with secondary TWW, control treatment function decreased rapidly while chemical treatment prolonged proper function of the drippers by maintaining a normal FR and coefficient of variation (CV). Wash treatment improved to some extent the irrigation function. Under irrigation with tertiary TWW the function of all treatments was significantly better than that of the secondary treatments. The total suspended solids level was found to be a significant factor in the mechanism of clogging formation according to biofouling development. The deposit chemical characterization could shed light on the mode of growth mechanism and properties of the biofouling. In general, oxidation treatments using hydrogen peroxide or hypochlorite acid were found to eliminate biofouling and in accordance also prevented clogging.

Evaluation of the activity of disinfectants against coliform bacteria group strains isolated from a sewage treatment plant (ETE-Ipanema)

Municipal wastewater usually presents pathogenic enteric bacteria, viruses and intestinal parasites. Primary, secondary and tertiary wastewater treatment eliminates 90-99.9% of these microorganisms and if a more efficient reduction of microorganisms is needed, disinfection with chemical compounds must be done. The extraordinary genetic variability of bacteria gives them adaptation ability against theses chemical agents, which indiscriminate use brings about serious health problems. In this study, chemical agents commonly used in disinfection procedures like chlorhexidine gluconate, sodium hypochlorite and quaternary ammonium compounds were investigated for their activity against bacteria from the coliform group, isolated from a sewage treatment plant, using the macrodilution method. It was observed that the addition of organic matter interferes in sensitivity levels and also that the lower the concentration and the exposure time, the higher the resistance. Sodium hypochlorite was the most effective against the coliforms, once inhibited their growth in every exposure time and at every disinfectant concentration used . Quaternary ammonium compounds and chlorhexidine gluconate were also effective, although a higher percentage of resistance was observed for both.

Retention of microplastics in a major secondary wastewater treatment plant in Vancouver, Canada

Municipal wastewater treatment plants (WWTPs) are conduits through which microplastics (MPs) are released into aquatic environments. However, the technical challenges in working with wastewater sample matrices have precluded reliable particle count budget calculations. We applied newly-adapted methods for MP collection and analysis to a study of a major WWTP serving a population of 1.3 million people near Vancouver, Canada. Suspected MP particles, including fibres, were counted and categorized using light microscopy in influent, primary effluent, secondary effluent, primary sludge and secondary sludge. Fourier Transform Infrared Spectroscopy (FT-IR) confirmed that just 32.4% of the suspected MPs were plastic polymers. Using FT-IR corrected data, we estimate that 1.76 ± 0.31 trillion MPs enter the WWTP annually, with 1.28 ± 0.54 trillion MPs settling into primary sludge, 0.36 ± 0.22 into secondary sludge, and 0.03 ± 0.01 trillion MPs released into the receiving environment. This corresponds to a retention of microplastics of up to 99% in the WWTP.

Modelling and optimisation of a multistage Reverse Osmosis processes with permeate reprocessing and recycling for the removal of N-nitrosodimethylamine from wastewater using Species Conserving Genetic Algorithms

The need for desalinated seawater and reclaimed wastewater is increasing rapidly with the rising demands for drinkable water required for the world with continuously growing population. Reverse Osmosis (RO) processes are now among the most promising technologies used to remove chemicals from industrial effluents. N-nitrosamine compounds and especially N-nitrosodimethylamine (NDMA) are human carcinogens and can be found in industrial effluents of many industries. Particularly, NDMA is one of the by-products of disinfection process of secondary-treated wastewater effluent with chloramines, chlorines, and ozone (inhibitors). However, multi-stage RO processes with permeate reprocessing and recycling has not yet been considered for the removal of N-nitrosodimethylamine from wastewater. This research therefore, begins by investigating a number of multi-stage RO processes with permeate-reprocessing to remove N-nitrosodimethylamine (NDMA) from wastewater and finds the best configuration in terms of rejection, recovery and energy consumption via optimisation. For the first time we have applied Species Conserving Genetic Algorithm (SCGA) in optimising RO process conditions for wastewater treatment. Finally, permeate recycling is added to the best configuration and its performance is evaluated as a function of the amount of permeate being recycled via simulation. For this purpose, a mathematical model is developed based on the solution diffusion model, which is used for both optimisation and simulation. A number of model parameters have been estimated using experimental data of Fujioka et al. (Journal of Membrane Science 454 (2014) 212–219), so that the model can be used for simulation and optimisation with high accuracy and confidence.

Advanced Oxidation with Nanofilm Photacatalyst’S on Stainless Steel Wire as Secondary Treatment of Wastewater

Advanced Oxidation with Nanofilm Photacatalyst’S on Stainless Steel Wire as Secondary Treatment of Wastewater

Characterization of Acinetobacter baumannii from water and sludge line of secondary wastewater treatment plant

The elimination of potentially pathogenic bacteria in wastewater treatment plants (WWTPs) attracts much attention in public health. Reports on the occurrence of the emerging hospital pathogen Acinetobacter baumannii in wastewaters do not include a continuous monitoring at all WWTP stages. The objective of this study was to characterize A. baumannii recovered from the water and sludge line of the secondary WWTP in Zagreb, Croatia over the period of one year. Recovery of A. baumannii was performed using CHROMagar Acinetobacter plates. Antimicrobial susceptibility testing was performed with broth microdilution and results interpreted using EUCAST breakpoints for clinical isolates of A. baumannii. Molecular characterization was performed by WGS and cgMLST. The secondary WWTP treating the urban wastewater is constantly receiving viable A. baumannii along with genes encoding carbapenem resistance, and emitting them via effluent into the environment. Furthermore, A. baumannii from influent are incorporated into activated sludge flocs in aeration basin. A. baumannii can survive the technological process of anaerobic mesophilic sludge digestion, and is finally destroyed in alkaline lime-treated stabilized sludge. The majority (102/119) of A. baumannii isolates were carbapenem-resistant, while antibiotic-susceptible isolates (17/119) were rarely recovered from all WWTP stages. Carbapenem-resistant isolates belonged to international clonal lineage IC2 carrying OXA-23 and IC1 carrying OXA-72, while the susceptible isolates belonged to IC5 or were unclustered. Increased resistance to antibiotics, together with the appearance of carbapenem- and even pandrug-resistant isolates in effluent as compared to influent wastewater, suggests the need of additional disinfection of effluent prior to its discharge into the natural recipient.

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

ABSTRACTTo 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.

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.