Impact of process design on greenhouse gas (GHG) generation by wastewater treatment plants

The overall on-site and off-site greenhouse gas emissions by wastewater treatment plants (WWTPs) of food processing industry were estimated by using an elaborate mathematical model. Three different types of treatment processes including aerobic, anaerobic and hybrid anaerobic/aerobic processes were examined in this study. The overall on-site emissions were 1952, 1992, and 2435 kg CO₂e/d while the off-site emissions were 1313, 4631, and 5205 kg CO₂e/d for the aerobic, anaerobic and hybrid treatment systems, respectively, when treating a wastewater at 2000 kg BOD/d. The on-site biological processes made the highest contribution to GHG emissions in the aerobic treatment system while the highest emissions in anaerobic and hybrid treatment systems were obtained by off-site GHG emissions, mainly due to on-site material usage. Biogas recovery and reuse as fuel cover the total energy needs of the treatment plants for aeration, heating and electricity for all three types of operations, and considerably reduce GHG emissions by 512, 673, and 988 kg CO₂e/d from a total of 3265, 6625, and 7640 kg CO₂e/d for aerobic, anaerobic, and hybrid treatment systems, respectively. Considering the off-site GHG emissions, aerobic treatment is the least GHG producing type of treatment contrary to what has been reported in the literature.     

Baffled membrane bioreactor (BMBR) for efficient nutrient removal from municipal wastewater

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance.     

The use of fortified soil-clay as on-site system for domestic wastewater purification

The quest for simple, low-cost and high-performance decentralized wastewater treatment system for domestic application in developing nations necessitated this study. Clay samples collected from different deposits in Nigeria were characterized by studying the mineralogical and geochemical composition using X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS), respectively. Three major clay minerals of kaolinite, illite and smectite were identified. The geochemical studies showed the abundance of SiO2, Al2O3 and H2O+ in each of the clay samples. Performance efficiency studies were conducted to determine the best combination ratio of pebbles/soil-clay. Soil-clay fortified by pebbles in combination ratios of 1:3 (i.e. pebbles:soil-clay = 1:3 (w/w) showed the optimum water purification, while the combination 3:1 gave the least. The flow rate studies showed that the wastewater had a longer residence time in non-fortified soil-clay than in fortified soil-clay. Two modes of treatment methods were employed-single and double column treatment methods (SCT and DCT). The two methods gave effluents of good quality characteristics, but those from the DCT were of better quality. The quality of effluents also varies from one clay type to another. The quality of effluents from media containing smectite clay mineral was better than those from other columns. Repeated usage of the fortified clay column showed a decrease of pH, TS and DO, and an increase of COD when monitored over a period of 10 days.     

Mercury mass balance at a wastewater treatment plant employing sludge incineration with offgas mercury control

Efforts to reduce the deliberate use of mercury (Hg) in modern industrialized societies have been largely successful, but the minimization and control of Hg in waste streams are of continuing importance. Municipal wastewater treatment plants are collection points for domestic, commercial, and industrial wastewaters, and Hg removal during wastewater treatment is essential for protecting receiving waters. Subsequent control of the Hg removed is also necessary to preclude environmental impacts. We present here a mass balance for Hg at a large metropolitan wastewater treatment plant that has recently been upgraded to provide for greater control of the Hg entering the plant. The upgrade included a new fluidized bed sludge incineration facility equipped with activated carbon addition and baghouse carbon capture for the removal of Hg from the incinerator offgas. Our results show that Hg discharges to air and water from the plant represented less than 5% of the mass of Hg entering the plant, while the remaining Hg was captured in the ash/carbon residual stream exiting the new incineration process. Sub-optimum baghouse operation resulted in some of the Hg escaping collection there and accumulating with the ash/carbon particulate matter in the secondary treatment tanks. Overall, the treatment process is effective in removing Hg from wastewater and sequestering it in a controllable stream for secure disposal.     

Nutrient loading on subsoils from on-site wastewater effluent, comparing septic tank and secondary treatment systems

The performance of six separate percolation areas was intensively monitored to ascertain the attenuation effects of unsaturated subsoils with respect to on-site wastewater effluent: three sites receiving septic tank effluent, the other three sites receiving secondary treated effluent. The development of a biomat across the percolation areas receiving secondary treated effluent was restricted on these sites compared to those sites receiving septic tank effluent and this created significant differences in terms of the potential nitrogen loading to groundwater. The average nitrogen loading per capita at 1.0 m depth of unsaturated subsoil equated to 3.9 g total-N/d for the sites receiving secondary treated effluent, compared to 2.1 g total-N/d for the sites receiving septic tank effluent. Relatively high nitrogen loading was, however, found on the septic tank sites discharging effluent into highly permeable subsoil that counteracted any significant denitrification. Phosphorus removal was generally very good on all of the sites although a clear relationship to the soil mineralogy was determined.     

Phosphatase activity in anaerobic bioreactors for wastewater treatment

Phosphatase (PO4ase) activity was investigated in continuous and fed-batch anaerobic bioreactors for wastewater treatment. PO4ase levels were high in continuously fed reactors (880-2632 micromol/L/h), compared to a fed-batch reactor (FBR) (540-1249 micromol/L/h). Alkaline and acid PO4ases were present in all the reactors, but in varying magnitudes and total PO4ase activity exhibited a 10-30% variation even at steady-state reactor conditions. The PO4ase activity was not affected by the inorganic phosphate (Pi) level in the reactors, but biomass level and wastewater type, including specific PO4ases (either alkaline or acid), strongly influenced the PO4ase activity in a reactor. Both flocculated and suspended cells produced PO4ase, and 60-65% of the enzyme was cell bound, remaining entrapped in the extracellular matrix and in cell-free form. Batch studies with anaerobic sludge showed a negative correlation between Pi and PO4ase activity. An increase in PO4ase activity was observed under starvation and higher salinity (above 15 g/L). Glucose and propionate (at 10 mM level) induced PO4ase activity, whereas acetate and butyrate (10 mM) addition had no response. This study also reveals that Archaea and bacteria contributed 45% and 55%, respectively, of total PO4ase activity in anaerobic sludge.     

Nitrogen removal from wastewater using membrane aerated microbial fuel cell techniques

Nitrogen removal mainly relies on sequential nitrification and denitrification in wastewater treatment. Microbial fuel cells (MFCs) are innovative wastewater treatment techniques for pollution control and energy generation. In this study, bench-scale wastewater treatment systems using membrane-aerated MFC (MAMFC) and diffuser-aerated MFC (DAMFC) techniques were constructed for simultaneous removal of carbonaceous and nitrogenous pollutants and electricity production from wastewater. During 210 days of continuous flow operation, when the dissolved oxygen (DO) in the cathodic compartment was kept at 2 mg/L, both reactors demonstrated high COD removal (>99%) and high ammonia removal (>99%) but low nitrogen removal (<20%). When a lower DO (0.5 mg/L) was maintained after day 121, both the MFC-based reactors still had excellent COD removal (>97%). However, the nitrogen removal of MAMFC (52%) was 2-fold higher than that of DAMFC (24%), indicating an enhanced performance of denitrification after DO reduction in the cathodic compartment of the MAMFC. Meanwhile, terminal restriction fragment length polymorphism (T-RFLP) analysis of ammonia-oxidizing bacteria (AOB) population in the MAMFC indicated the diversity of AOB with equally important Nitrosospira and Nitrosomonas species present in the cathodic biofilm after DO reduction. The average voltage output in the MAMFC was significantly higher than that in DAMFC under both DO conditions. The results suggest that MAMFC systems have the potential for wastewater treatment with improved nitrogen removal and electricity production.     

Persistence and prevalence of pathogenic and extended-spectrum beta-lactamase-producing Escherichia coli in municipal wastewater treatment plant receiving slaughterhouse wastewater

We compared the prevalence of pathogenic and extended-spectrum beta-lactamase (ESBL) – producing Escherichia coli in effluents of a municipal wastewater treatment plant (WWTP) receiving wastewater from a slaughterhouse. A total of 1248 isolates were screened for the presence of virulence genes associated with enterohemorrhagic E. coli (EHEC) (stx₁, stx₂, and eae) and extraintestinal pathogenic E. coli (ExPEC) (sfa/focDE, kpsMT K1, hlyA, papEF, afa/draBC, clbN, f17A and cnf). The prevalence of atypical enteropathogenic E. coli (EPEC) was 0.7%, 0.2% and 0.5% in city wastewater, slaughterhouse wastewater and in the treated effluent, respectively. One stx_1a and stx_2b-positive E. coli isolate was detected in city wastewater. The prevalence of ExPEC was significantly higher in city wastewater (8.4%), compared to slaughterhouse wastewater (1.2%). Treatment in the WWTP did not significantly impact the prevalence of ExPEC in the outlet effluent (5.0%) compared to city wastewater. Moreover, the most potentially pathogenic ExPEC were isolated from city wastewater and from the treated effluent. ESBL-producing E. coli was also mainly detected in city wastewater (1.7%), compared to slaughterhouse wastewater (0.2%), and treated effluent (0.2%). One ESBL-producing E. coli, isolated from city wastewater, was eae-β1 positive. These results showed that pathogenic and/or ESBL-producing E. coli were mainly detected in human wastewater, and at a lesser extend in animal wastewater. Treatment failed to eliminate these strains which were discharged into the river, and then these strains could be transmitted to animals and humans via the environment.     

State estimation for large-scale wastewater treatment plants

Many relevant process states in wastewater treatment are not measurable, or their measurements are subject to considerable uncertainty. This poses a serious problem for process monitoring and control. Model-based state estimation can provide estimates of the unknown states and increase the reliability of measurements. In this paper, an integrated approach is presented for the optimization-based sensor network design and the estimation problem. Using the ASM1 model in the reference scenario BSM1, a cost-optimal sensor network is designed and the prominent estimators EKF and MHE are evaluated. Very good estimation results for the system comprising 78 states are found requiring sensor networks of only moderate complexity.     

Toxicity of fluoride to microorganisms in biological wastewater treatment systems

Fluoride is a common contaminant in a variety of industrial wastewaters. Available information on the potential toxicity of fluoride to microorganisms implicated in biological wastewater treatment is very limited. The objective of this study was to evaluate the inhibitory effect of fluoride towards the main microbial populations responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of short-term batch bioassays indicated that the toxicity of sodium fluoride varied widely depending on the microbial population. Anaerobic microorganisms involved in various metabolic steps of anaerobic digestion processes were found to be very sensitive to the presence of fluoride. The concentrations of fluoride causing 50% metabolic inhibition (IC₅₀) of propionate- and butyrate-degrading microorganisms as well as mesophilic and thermophilic acetate-utilizing methanogens ranged from 18 to 43 mg/L. Fluoride was also inhibitory to nitrification, albeit at relatively high levels (IC₅₀ = 149 mg/L). Nitrifying bacteria appeared to adapt rapidly to fluoride, and a near complete recovery of their metabolic activity was observed after only 4 d of exposure to high fluoride levels (up to 500 mg/L). All other microbial populations evaluated in this study, i.e., glucose fermenters, aerobic glucose-degrading heterotrophs, denitrifying bacteria, and H₂-utilizing methanogens, tolerated fluoride at very high concentrations (>500 mg/L).     

Minimization of excess sludge production for biological wastewater treatment

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.     

Reduction of endocrine disruptor emissions in the environment: The benefit of wastewater treatment

The occurrence and fate of four estrogens and five alkylphenolic compounds were studied in thirteen plants with various treatment processes, sizes and countries. Complete load mass balance, including water and sludge phases, has shown a high reduction of the total load of hormones, around 90%. The removal of alkylphenols was more variable, due to the degradation of nonylphenol (NP) precursors - alkylphenol polyethoxylates (APnEO) - during the treatment, resulting in significant production of shorter and toxic alkylphenols (NP and short polyethoxylates) that concentrate in the sludges. Under anaerobic conditions, such as anaerobic digestion process, the load of NP was in most cases observed to increase. When considering the environmental impact, the high reduction of endocrine disrupting compounds (EDC) concentrations between raw wastewater and effluent enables to satisfy the requirements of the Water Framework Directive for NP except in very critical situations where the dilution factor of the effluent in the river would be lower than 7. For sludges, the pending European Directive on spreading of sludge on land would be complied with in all cases.     

Membrane coupled high-performance compact reactor: a new MBR system for advanced wastewater treatment

This study examined the potential and limitations of a new submerged membrane system coupled with a High-performance Compact Reactor (HCR) to take advantages of both systems. The configuration and installation position in the HCR of the membrane module were thoroughly investigated for the optimum design of a submerged membrane coupled with HCR, e.g., MHCR. Inside the draft tube proved to be better location rather than outside the draft tube or in the degas tank and an open-type configuration of a membrane module has an advantage over a fixed-type configuration in terms of membrane fouling. Comparison of the innovative MHCR with a conventional membrane bioreactor (MBR) was made to identify and prove the superiority of MHCR to MBR with respect to the membrane performance. The MHCR has shown the great potential, particularly for the treatment of wastewater of high organic strength.     

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

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

Antimicrobial resistance of fecal indicators in municipal wastewater treatment plant

Antimicrobial resistance of fecal coliforms (n = 153) and enterococci (n = 199) isolates was investigated in municipal wastewater treatment plant (WWTP) based on activated sludge system. The number of fecal indicators (in influent and effluent as well as in the aeration chamber and in return activated sludge mixture) was determined using selective media. Susceptibility of selected strains was tested against 19 (aminoglycosides, aztreonam, carbapenems, cephalosporins, β-lactam/β-lactamase inhibitors, fluoroquinolones, penicillines, tetracycline and trimethoprim/sulfamethoxazole) and 17 (high-level aminoglycosides, ampicillin, chloramphenicol, erythromycin, fluoroquinolones, glycopeptides, linezolid, lincosamides, nitrofuration, streptogramins, tetracycline) antimicrobial agents respectively. Among enterococci the predominant species were Enterococcus faecium (60.8%) and Enterococcus faecalis (22.1%), while remaining isolates belonged to Enterococcus hirae (12.1%), Enterococcus casseliflavus/gallinarum (4.5%), and Enterococcus durans (0.5%). Resistance to nitrofuration and erythromycin was common among enterococci (53% and 44%, respectively), and followed by resistance to ciprofloxacin (29%) and tetracycline (20%). The resistance phenotypes related to glycopeptides (up to 3.2%) and high-level aminoglycosides (up to 5.4%) were also observed. Most frequently, among Escherichia coli isolates the resistance patterns were found for ampicillin (34%), piperacillin (24%) and tetracycline (23%). Extended-spectrum β-lactamase producing E. coli was detected once, in the aeration chamber. In the study the applied wastewater treatment processes considerably reduced the number of fecal indicators. Nevertheless their number in the WWTP effluent was higher than 10⁴ CFU per 100 ml and periodically contained 90% of bacteria with antimicrobial resistance patterns. The positive selection of isolates with antimicrobial resistance patterns was observed during the treatment processes. Substantial concern should be paid to the isolates resistant to 3 or more chemical classes of antimicrobials (MAR). In treated wastewater MAR E. coli and MAR enterococci constituted respectively 9% and 29% of tested isolates.     

Usage of fuzzy modeling for cultivation of forests irigated by wastewater treatment plants

Cultivation of forests and plant species by utilizing processed wastewater and sludge from the wastewater treatment plants is an effective method to reduce the release of harmful substances and provide favorable conditions for the development of agricultural sector under the shortage of water resources. For this purpose, the experiments have been carrying out to investigate the ability of species to absorb chemical elements under increased concentrations in wastewater, as well as other characteristics and features of species’ behavior in biological, chemical and physical aspects. The behavior is a result of complex cause‐effect dynamical interactions in ecological networks with unknown mathematical models of underlying functional relationships. There are two important features inherent in the investigation of cultivating species by processed wastewater: empirical modeling of species’ behavior and qualitative reasoning with imprecise information about this behavior.

Proceeding from analysis of chains of interactions viewed as functional mappings between factors and investigated objects, the paper proposes a solution to the development of fuzzy modeling tools to support the investigation process. The proposed architecture includes the following components: a model that describes an ecological network under investigation; artificial neural network modules that model complex direct cause‐effect interactions; a fuzzy inference system that provides the investigator with qualitative reasoning about these interactions within a framework of the model; and control system that, under the requests from the investigator, controls the operation of the above components.     

Economic feasibility study for wastewater treatment: A cost-benefit analysis

Water resource management should be made from a multidisciplinary perspective. In this sense, economic research into the design and implementation of policies for the efficient management of water resources has been emphasized by the European Water Framework Directive (WFD). Cost-benefit analysis (CBA) is one of the more widely accepted economic instruments since it is a rational and systematic decision-making support tool. Moreover, the wastewater treatment process has significant associated environmental benefits. However, these benefits are often left uncalculated because they have no market value. In this paper, using the concept of shadow price, a quantification of the environmental benefits derived from wastewater treatment is made. Once the environmental benefits are estimated and the economic costs of the treatment processes are known, a CBA is made for each of the wastewater treatment plants (WWTPs) under study. In this way, a useful economic feasibility indicator is obtained for WWTP operation.     

Economic evaluation of alternative wastewater treatment plant options for pulp and paper industry

Excessive water consumption in pulp and paper industry results in high amount of wastewater. Pollutant characteristics of the wastewater vary depending on the processes used in production and the quality of paper produced. However, in general, high organic material and suspended solid contents are considered as major pollutants of pulp and paper industry effluents. The major pollutant characteristics of pulp and paper industry effluents in Turkey were surveyed and means of major pollutant concentrations, which were grouped in three different pollution grades (low, moderate and high strength effluents), and flow rates within 3000 to 10,000 m³/day range with 1000 m³/day steps were used as design parameters. Ninety-six treatment plants were designed using twelve flow schemes which were combinations of physical treatment, chemical treatment, aerobic and anaerobic biological processes. Detailed comparative cost analysis which includes investment, operation, maintenance and rehabilitation costs was prepared to determine optimum treatment processes for each pollution grade. The most economic and technically optimal treatment processes were found as extended aeration activated sludge process for low strength effluents, extended aeration activated sludge process or UASB followed by an aeration basin for medium strength effluents, and UASB followed by an aeration basin or UASB followed by the conventional activated sludge process for high strength effluents.     

Occurrence and fate of TMDD in wastewater treatment plants in Germany

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

Life cycle assessment of ecological sanitation system for small-scale wastewater treatment

Ecological sanitation (EcoSan) concepts, relying on an environmentally sound management of water, nutrient and energy fluxes, have been poorly characterized in literature and are widely ignored by public planning authorities, architects or engineers. A comparative life cycle assessment (LCA) of an EcoSan system at an office building and of conventional systems was carried out in order to provide practical data and information to (partially) fill this gap. Compared to conventional systems, EcoSan can reduce the contribution to ecosystem quality damage by more than 60%. EcoSan leads, however, to higher damages on resources and human health and higher impact on climate change. Key improvement possibilities and research needs related to these results are discussed throughout the paper. Ecological sanitation appears to be a promising alternative to small-scale wastewater treatment. At higher scales, low water consumption conventional systems are better performing and are not likely to be replaced by EcoSan systems in the short term. Standard conventional systems have very poor environmental performances and should be upgraded as far as possible.