Aerobic Wastewater Treatment Plants Research Articles

Impact of long-term temperature shifts on activated sludge microbiome dynamics and micropollutant removal

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4–40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.

Aquatic aerobic biodegradation of commonly flushed materials in aerobic wastewater treatment plant solids

Microfibers and microplastics originating from wastewater treatment plant (WWTP) effluents are significant pollutants in freshwater sources and marine environments. This research investigated the biodegradation of cotton microfibers generated from bleached cotton jersey knit fabric and commercially available flushable wipes, polypropylene-based (PP) nonwoven wipes containing a cellulose component, and tissue paper. Biodegradation was tested in wastewater treatment plants (WWTP) solids, seawater, and lakewater according to the ISO 14852 and ASTM D6691 standard methods in an ECHO respirometer. Degradation experiments continued until a plateau in CO2 emissions was reached, and the final biodegradation extent was calculated relative to the theoretical CO2 produced based on elemental analysis. The results showed that the cotton and other cellulosic materials/components biodegrade to a great extent, as expected for all conditions, whereas the PP did not degrade. In general, for the cellulose polypropylene composite wipes, the cellulose biodegraded readily; the presence of the PP did not hinder the cellulose biodegradation.

Assessment of Diclofenac Adsorption into Activated Sludge: Mechanism and Thermodynamic

This study aimed at understanding and characterizing the sorption process of Diclofenac (DCF) onto activated sludge under conditions similar to those of a conventional Wastewater Treatment Plant (WWTP). Two experiments were performed: kinetics test, composed of six identical pairs of control/sample with the same DCF concentration stirred under constant rotation for different intervals; and an adsorption thermodynamics test with one pair of control samples and six duplicate samples with DCF concentrations from 5 - 100 mg L-1 stirred under constant rotation for the same period. DCF concentrations in the supernatant were measured in time spectrophotometrically at 282 nm. The adsorption of diclofenac onto the activated sludge reached its equilibrium after approximately 2 hours. The results showed that the process was best described by the Freundlich and Langmuir isotherm models, which suggest that the adsorption of DCF onto the activated sludge is a non-favorable second order reaction with a monolayer coverage. The Temkin isotherm model suggests that the heat of adsorption of the DCF molecules in the layer decreases linearly as a result of the increased surface coverage and follows a chemisorption mechanism. The amount of DCF adsorbed onto the sludge particles varied between 17 and 44%, with the adsorption ratio of DCF per gram of sludge being considerably low (< 1 mg per g of sludge). This might be a result of the longer hydraulic retention times (HRT) adopted, considering that DCF may be toxic to the sludge microbiota, interfering with DCF removal from the supernatant. Thus, improving diclofenac removal by aerobic WWTP might require an adjustment of HRT to enhance sorption onto the sludge and reduce its impact on bacterial community.

Imprints of Lockdown and Treatment Processes on the Wastewater Surveillance of SARS-CoV-2: A Curious Case of Fourteen Plants in Northern India

The present study investigated the detection of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) genomes at each treatment stage of 14 aerobic wastewater treatment plants (WWTPs) serving the major municipalities in two states of Rajasthan and Uttarakhand in Northern India. The untreated, primary, secondary and tertiary treated wastewater samples were collected over a time frame ranging from under-lockdown to post-lockdown conditions. The results showed that SARS-CoV-2 RNA was detected in 13 out of 40 wastewater samples in Jaipur district, Rajasthan and in 5 out of 14 wastewater samples in the Haridwar District, Uttarakhand with the E gene predominantly observed as compared to the N and RdRp target genes in later time-points of sampling. The Ct values of genes present in wastewater samples were correlated with the incidence of patient and community cases of COVID-19. This study further indicates that the viral RNA could be detected after the primary treatment but was not present in secondary or tertiary treated samples. This study implies that aerobic biological wastewater treatment systems such as moving bed biofilm reactor (MBBR) technology and sequencing batch reactor (SBR) are effective in virus removal from the wastewater. This work might present a new indication that there is little to no risk in relation to SARS-CoV-2 while reusing the treated wastewater for non-potable applications. In contrast, untreated wastewater might present a potential route of viral transmission through WWTPs to sanitation workers and the public. However, there is a need to investigate the survival and infection rates of SARS-CoV-2 in wastewater.

Simulating behavior of petroleum compounds during refinery effluent treatment using the SimpleTreat model

Distribution and elimination of petroleum products can be predicted in aerobic wastewater treatment plants (WWTPs) using models such as multimedia fate model SimpleTreat. An advantage of the SimpleTreat model is that it only requires a few basic properties of a chemical in wastewater to calculate partitioning, biodegradation and ultimately emissions to air, surface water and produced sludge. The SimpleTreat model structure reflects a WWTP scheme. However, refinery WWTPs typically incorporate more advanced treatment processes such as dissolved air flotation (DAF), a process that clarifies wastewaters by the removal of suspended matter such as oil or solids. The objective of this work was to develop a WWTP removal model that includes DAF treatment. To understand how including a DAF in the model affects the predicted concentrations of petroleum constituents in effluent, we replaced the primary sedimentation module in SimpleTreat with a module simulating DAF. Subsequently, we compared results from the WWTP-DAF model with results obtained with the original SimpleTreat model for a library of over 1500 representative hydrocarbon constituents. The increased air-water exchange in a WWTP-DAF unit resulted in higher predicted removal of volatile constituents. Predicted removal with DAF was on average 17% larger than removal with primary sedimentation. We compared modelled results with measured removal data from the literature, which supported that this model refinement continues to improve the technical basis of assessment of petroleum products.

The influence of solid-liquid coefficient in the fate of pharmaceuticals and personal care products in aerobic wastewater treatment.

Wastewater treatment plants (WWTPs) are considered to be a source of environmental contamination by micropollutants, especially from pharmaceuticals and personal care products (PCPs). The pathway of those compounds during sewage treatment has been investigated, but data from real-scale WWTPs is still missing (for example, the values of the solid-liquid coefficient (Kd) during treatment). This paper uses the Kd values for some pharmaceuticals and PCPs (fenofibrate, gemfibrozil, propranolol, metoprolol, salicylic acid, acetylsalicylic acid, ibuprofen, diclofenac, naproxen, fenoprofen, caffeine, triclosan, methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben) to describe the micropollutants' behavior in the treatment process. In order to attain this data, an aerobic wastewater treatment plant located in Brazil was studied. Six samplings were carried out and a mass balance was performed, associating the concentrations of the micropollutants in the liquid phase with the solid phase (sludge and suspended solids). Of all the compounds analyzed, caffeine was the most biodegradable pollutant, as almost 98% of its mass was biodegraded. In contrast, triclosan had the highest load in sludge (median of 163.0mgday-1) and adsorbed in SS (median of 0.593mgday-1) at the output. Summing up, each micropollutant had a specific way to be removed during wastewater treatment.

Aerobic biodegradation of 2 fluorotelomer sulfonamide-based aqueous film-forming foam components produces perfluoroalkyl carboxylates.

The biodegradation of 2 common fluorotelomer surfactants used in aqueous film forming foams (AFFFs), 6:2 fluorotelomer sulfonamide alkylamine (FTAA) and 6:2 fluorotelomer sulfonamide alkylbetaine (FTAB), was investigated over 109 d with aerobic wastewater-treatment plant (WWTP) sludge. Results show that biodegradation of 6:2 FTAA and 6:2 FTAB produces 6:2 fluorotelomer alcohol (FTOH), 6:2 fluorotelomer carboxylic acid (FTCA), 6:2 fluorotelomer unsaturated carboxylic acid (FTUCA), 5:3 FTCA, and short-chain perfluoroalkyl carboxylates (PFCAs). Additional degradation products included 6:2 fluorotelomer sulfonamide (FTSAm), which was a major degradation product in the presence of either active or sterilized sludge, whereas 6:2 fluorotelomer sulfonate (FTSA) production was measured with sterilized sludge only. Six additional degradation products were tentatively identified by quadrupole time-of-flight mass spectrometry (qTOF-MS) and attributed to N-dealkylation and oxidation of 6:2 FTAA. Environ Toxicol Chem 2017;36:2012-2021. © 2017 SETAC.

Chemical pre-treatment of fugate from biogas stations

Dealing with the digestate liquid phase from biogas stations has become a problem, due to the rapidly increasing number of biogas stations, tighter legislation, and the nature of the digestate that remains after anaerobic digestion of a biodegradable feedstock. The present solution is a farmland disposal. Standard biological treatment is not applicable because of the extremely high Chemical Oxygen Demand (COD). The method proposed here places chemical pre-treatment of the digestate before the biological stage. This reduces the COD to an acceptable level, from about 100 kg m−3 to about (2–4) kg m−3. The separated water phase can then be treated in a standard biological aerobic wastewater treatment plant. The chemical sludge can be treated by composting, together with the biological sludge. With the use of proper additives, a digestate material can be produced that raises the fertilizing and adsorption properties of the soil.

Sustainable operation of a biological wastewater treatment plant

The sustainable operation of a biological wastewater treatment plant is significantly linked to its removal efficiency, cost of sludge management, energy consumption and monitoring cost. The biological treatment offers high organic removal efficiency, it also entails significant sludge production, which contains active (live) and inactive (dead) microorganisms and must be treated prior to final disposal, in order to prevent adverse impact on public health and environment. The efficiency of the activated sludge treatment process is correlated to an efficient solid-liquid separation, which is strongly depended on the biomass settling properties. The most commonly encountered settling problems in a wastewater treatment plant, which are usually associated with operating conditions and specific microorganisms growth, are sludge bulking, floating sludge, pin point flocs and straggler flocs. Sustainable management of sludge and less energy consumption are the two principal aspects that determine the operational cost of wastewater treatment plants. Sludge treatment and management accumulate more than 50% of the operating cost. Aerobic wastewater treatment plants have high energy requirements for covering the needs of aeration and recirculations. In order to ensure wastewater treatment plants’ effective operation, a large number of physicochemical parameters have to be monitored, thus further increasing the operational cost. As the operational parameters are linked to microbial population, a practical way of wastewater treatment plants’ controlling is the microscopic examination of sludge, which is proved to be an important tool for evaluating plants’ performance and assessing possible problems and symptoms. This study presents a biological wastewater treatment plant with almost zero biomass production, less energy consumption and a practical way for operation control through microbial manipulation and microscopic examination.

Life Cycle Assessment to Identify Environmental Improvements in an Aerobic Waste Water Treatment Plant

Life Cycle Assessment to Identify Environmental Improvements in an Aerobic Waste Water Treatment Plant

Occurrence and activity of sulphate reducing bacteria in aerobic activated sludge systems.

In the sewage or wastewater treatment plant, biological sulphate reduction can occur spontaneously or be applied beneficially for its treatment. The results of this study can be applied to control SRB in the sewage and WWTP. Therefore, population diversity analyses of SRB for nine activated sludge wastewater treatment plants (WWTP) in the Netherlands and the effect of long-term (months) oxygen exposures on the SRB activity were carried out. T-RFLP and clone sequencing analyses of winter and summer samples revealed that (1) all WWTP have a similar SRB population, (2) there is no seasonal impact (10-20 °C) on the SRB population present in the WWTP and (3) Desulfobacter postgatei, Desulfovibrio desulfuricans and Desulfovibrio intestinalis were the most common and dominant SRB species observed in these samples, and origin from the sewage. Short term activity tests demonstrated that SRB were not active in the aerobic WWTP, but while flushed with N2-gas SRB became slightly active after 3 h. In a laboratory reactor at a dissolved oxygen concentration of <2 %, sulphate reduction occurred and 89 % COD removal was achieved. SRB grew in granules, in order to protect themselves for oxygen exposures. SRB are naturally present in aerobic WWTP, which is due to the formation of granules.

Effect of Alternative Nutrient Sources During Anaerobic Degradation of Potato Wastewater

The supplementation of nutrients on biological wastewater treatment in many cases may become a relevant part of the treatment cost. In that sense, the finding of new efficient and economic nutrient sources is very important in large scale industrial applications. This work reports on the effect of four readily available alternative nutrient sources during anaerobic degradation of potato wastewater: Peptone, soybean meal, sludge from an aerobic wastewater treatment plant (aerobic sludge) and NH 4 NO 3 plus Micronutrient Supplementation (MS). The addition of alternative nutrient sources changed the rate limiting step from the last steps to hydrolysis in all the cases. While the added soybean meal allowed obtaining the higher final conversion, the degradation rate was slower than the non-supplemented control. The assays with NH4NO3+MS as nitrogen source presented the highest degradation rate. Moreover both NH4NO3 and MS are needed to improve the degradation rates. The percentage of residual COD after treatment was similar for peptone, aerobic sludge and NH4NO3+MS test. However, the lowest percentage of residual soluble COD was obtained when the aerobic sludge was used as supplement. The aerobic sludge presented Co and Mo deficiencies. Finally, taking into account the advantages and disadvantages discussed, among those tested, the aerobic sludge seems to be the best alternative nutrient source for industrial applications.

Urban Waste Management and Potential Agricultural Use in South American Developing Countries: A Case Study of Chimborazo Region (Ecuador)

In South America, a high percentage of urban waste streams are not well managed, implying associated health and environmental risks. In Ecuador, around 2.7 million tons of municipal solid wastes (MSW) are generated annually, with 80 percent located in urban areas. Correct management and hygienic and ecological issues from these increased quantities of waste is the responsibility of municipalities that must provide sewerage, wastewater treatment, and solid waste management, according to the Constitution of the Republic (Art 264). With only seven licensed landfill areas out of thirty-one in total (66 percent mechanized and 34 percent manually sorted), a sustainable waste management model must be developed to reduce environmental hazards and also to obtain new bioproducts such as compost or fertilizers. Agricultural utilization of MSW compost is the most cost-effective management option compared to traditional means such as landfilling or incineration, and this option also enables the recycling of potential plant nutrients. In this work, the problem we addressed was to obtain analytical information about representative MSW samples from different origins and locations within the Chimborazo region in order to establish its potential for composting. In the studied MSW samples (which included sludge from aerobic wastewater treatment plants), high nutrient contents and low concentrations of heavy metals were observed, showing great potential to develop high-quality compost. In addition, improvement of separate collections of food market and/or municipal gardening wastes can provide specific clean waste streams of degradable materials to be managed separately from not separately collected MSW.

Alternatives for energy production in aerobic wastewater treatment facilities

Using technologies such as anaerobic digestion for energy generation from wastewater demands a change in infrastructure that several treatment works are not prepared to immediately implement. This works explores the use of energy production technologies to increase the sustainability of conventional aerobic wastewater treatment plants. The first option considered sludge (a by-product from wastewater treatment) as raw material for biodiesel production as Fatty Acid Methyl Esters (FAME). The second option consisted of the addition of microalgae during aerobic wastewater treatment and subsequent harvesting of combined microalgae-sludge to produce biodiesel. Results showed that microalgae were able to grow in aerobic wastewater treatment reactors, reaching maximum growth after 6 days. The use of microalgae did not statistically affect chemical oxygen demand removal but provided benefits on ammonia removal (100% removal vs 68 ± 9% when microalgae were not added). Activated sludge contained fewer lipids (13 ± 3%, by dry weight) than the microalgae-sludge mixture (20.8 ± 4.5%). Hence, FAME production when using microalgae-sludge was higher (51.12 ± 12 mg of FAME/g of dry microalgae-sludge) than when using activated sludge (25.6 ± 7 mg of FAME/g of dry activated sludge). This work showed that producing biodiesel from microalgae grown in conjunction with bacteria during aerobic wastewater treatment can reduce energy use and carbon emissions produced by 18.6 and 26.5%, respectively.

Development of an analytical microbial consortia method for enhancing performance monitoring at aerobic wastewater treatment plants

An analytical method to produce profiles of bacterial biomass fatty acid methyl esters (FAME) was developed employing rapid agitation followed by static incubation (RASI) using selective media of wastewater microbial communities. The results were compiled to produce a unique library for comparison and performance analysis at a Wastewater Treatment Plant (WWTP). A total of 146 samples from the aerated WWTP, comprising 73 samples of each secondary and tertiary effluent, were included analyzed. For comparison purposes, all samples were evaluated via a similarity index (SI) with secondary effluents producing an SI of 0.88 with 2.7% variation and tertiary samples producing an SI 0.86 with 5.0% variation. The results also highlighted significant differences between the fatty acid profiles of the tertiary and secondary effluents indicating considerable shifts in the bacterial community profile between these treatment phases. The WWTP performance results using this method were highly replicable and reproducible indicating that the protocol has potential as a performance-monitoring tool for aerated WWTPs. The results quickly and accurately reflect shifts in dominant bacterial communities that result when processes operations and performance change.

Comparative performance evaluation of full-scale anaerobic and aerobic wastewater treatment processes in Brazil

This article evaluates and compares the actual behavior of 166 full-scale anaerobic and aerobic wastewater treatment plants in operation in Brazil, providing information on the performance of the processes in terms of the quality of the generated effluent and the removal efficiency achieved. The observed results of effluent concentrations and removal efficiencies of the constituents BOD, COD, TSS (total suspended solids), TN (total nitrogen), TP (total phosphorus) and FC (faecal or thermotolerant coliforms) have been compared with the typical expected performance reported in the literature. The treatment technologies selected for study were: (a) predominantly anaerobic: (i) septic tank + anaerobic filter (ST + AF), (ii) UASB reactor without post-treatment (UASB) and (iii) UASB reactor followed by several post-treatment processes (UASB + POST); (b) predominantly aerobic: (iv) facultative pond (FP), (v) anaerobic pond followed by facultative pond (AP + FP) and (vi) activated sludge (AS). The results, confirmed by statistical tests, showed that, in general, the best performance was achieved by AS, but closely followed by UASB reactor, when operating with any kind of post-treatment. The effluent quality of the anaerobic processes ST + AF and UASB reactor without post-treatment was very similar to the one presented by facultative pond, a simpler aerobic process, regarding organic matter.

Monitoring of di-(2-ethylhexyl)phthalate, nonylphenol, nonylphenol ethoxylates, and polychlorinated biphenyls in anaerobic and aerobic sewage sludge by gas chromatography–mass spectrometry

The occurrence of di-(2-ethyhexyl)phthalate (DEHP), nonylphenol and nonyphenol mono- and diethoxylates (NPEs) and seven polychlorinated biphenyl (PCB) congeners in different types of sludge samples is reported. The analysis of these compounds was carried out by sonication-assisted extraction and analytical determination by gas chromatography coupled with a mass spectrometry detector, following a previously described method. The applicability of the method was tested by monitoring the organic pollutants in primary, secondary, mixed, and digested-dehydrated sludge samples from two wastewater treatment plants (WWTPs) based on aerobic and on anaerobic biological stabilization. The occurrence of these compounds in sewage sludge and the influence of sludge stabilization process on the further farmland application of the sludge were evaluated. DEHP and NPEs were detected in all analysed sludge samples from both WWTPs at concentration levels in the range of 22.3–601 mg kg−1 and 136–2357 mg kg−1 dm (dry matter), respectively. PCBs were detected in all types of sludge analysed from the anaerobic WWTP but was not detected in any sludge sample from the aerobic WWTP. Concentration levels of the sum of the seven PCBs congeners were up to 1.5 mg kg−1 dm. The concentration of DEHP, sum of NPEs, and sum of the seven PCB congeners were higher than the limits fixed in the third draft of the future Sludge Directive for land application of sludge in the 67%, 100%, and 11% of samples from the anaerobic WWTP and in the 83%, 92%, and 0% of samples from the aerobic WWTP, respectively.

Sludge Reduction by Predatory Activity of Aquatic Oligochaetes in Wastewater Treatment Plants: Science or Fiction? A Review

Biological aerobic wastewater treatment plants (WWTPs) produce a lot of excess sludge. The costs for handling this residual product are increasing, so the search for alternative techniques to reduce the amount of sludge has to be continued. Activated sludge consists of inorganic and organic substances, bacteria, protozoa and metazoa. Due to incomplete biomass conversion, sludge consumption yields less oligochaete biomass. From a technological point of view, the application of aquatic oligochaetes to reduce the sludge production offers interesting perspectives. This paper aims to review the feasibility for the reduction of activated sludge in WWTPs by means of aquatic oligochaetes. Also the current techniques concerning sludge reduction are taken into account. Several of the WWTPs relevant parameters, which may influence predatory activity of aquatic oligochaetes, are discussed: particle size, organic content of substrate, bacteria preference, life cycle and population dynamics of aquatic oligochaetes, temperature, pH, oxygen and process conditions. From the literature it appeared that most research has been performed on laboratory scale. Only a few authors mention a significant reduction of the sludge production by ‘sessile’ species such as Lumbriculus. Vermicultures for the reduction of activated sludge are rather common in developing countries. Incidentally large annelid blooms have been noticed in WWTPs. It remains obscure which factors trigger the initiation of annelid blooms in WWTPs and which are of importance to maintain a stable annelid population in WWTPs. The influence of a considerable worm bloom on the waste sludge production is still under investigation.

LABORATORY-SCALE TRIALS OF ELECTROLYTIC TREATMENT ON INDUSTRIAL WASTEWATERS: MICROBIOLOGICAL ASPECTS

ABSTRACT Animal, civil and industrial waste matter is a source of potential chemical, microbiological and air pollutants. In populated areas the presence of faecal bacteria and the production of malodorous compounds during waste storage and in the tanks of wastewater treatment plants, can cause concern. The general aim of the work was to study electrolytic waste treatment (recently applied on animal slurry) using low electric current across graphite and copper electrodes, determining its effect on the microflora of sludge, collected from the equalisation basin of an industrial aerobic wastewater treatment plant, and on odour emission abatement. Biochemical and enzymatic indicators like ATP content and a pool of 19 enzymatic activities were tested, comparing them with viable cell counts by traditional microbiological methods, to verify the validity of such indicators in monitoring the electrolytic treatment and to assess their correlation with odour reduction. The preliminary results of our laboratory-scale trials showed that in the presence of inert electrodes, such as graphite, metabolic activity is stimulated, whereas with copper electrodes the ATP content and some enzymatic activities are inhibited quite considerably after only four days, this being accompanied by a marked reduction in odour. Consideration was also given to the total copper released from the electrodes and its recovery using iron electrodes.

Microbially influenced corrosion on stainless steel in waste water treatment plants: Part 2

Microbially influenced corrosion (MIC)on stainless steel in freshwater is commonly related to the development of an active biofilm on the surface. A known effect of the microbial activity that causes the formation of a biofilm on stainless steel surfaces is the ennoblement of the stainless steel, as shown in the field test presented in part 1 of this study. Ennoblement may increase the risk of local corrosion if the potential rises above the breakdown potential of the passive layer for the steel grade. An aim of this investigation was to examine the reasons for corrosion when ennoblement occurs on stainless steels and to provide guidance on the use of particular grades of stainless steel in the final stages of waste water treatment systems operating under aerobic conditions. In this paper (part 2), the corrosion resistance of stainless steels in distilled waters containing various amounts of chlorides, nitrates, and sulphates has been evaluated according to a factorial design. A risk window was then designed for predicting MIC on stainless steel in aerobic waste water treatment plants based on these results. Another aim of the investigation, carried out in a waste water treatment plant, was to test coupons with residual weld oxides on the surface and to compare the corrosion resistance with pickled welded coupons. All coupons were exposed in the final stage of the plant where no ennoblement of the open circuit potential occurred in the beginning. Nevertheless, after several weeks, high potentials were recorded following heavy rainfall. After field test, visual inspection revealed corrosion on AISI 304 stainless steel.