Influent concentrations and removal performances of metals through municipal wastewater treatment processes

An update on sustainabilities and challenges on the removal of ammonia from aqueous solutions: A state-of-the-art review

An insightful attempt has been made in this review and the primary objective was to meticulously provide an update on the sustainabilities, advances and challenges pertaining the removal of ammonia from water and wastewater. Specifically, ammonia is a versatile compound that prevails in various spheres of the environment, and if not properly managed, this chemical species could pose severe ecological pressure and toxicity to different receiving environments and its biota. The notorious footprints of ammonia could be traced to anoxic conditions, an infestation of aquatic ecosystems, hyperactivity, convulsion, and methaemoglobin, popularly known as the "blue baby syndrome". In this review, latest updates regarding the sustainabilities, advancements and challenges for the removal of ammonia from aqueous solutions, i.e., river and waste waters, are briefly elucidated in light of future perspectives. Viable routes and ideal hotspots, i.e., wastewater and drinking water, for ammonia removal under the cost-effective options have been unpacked. Key mechanisms for the removal of ammonia were grossly bioremediation, oxidation, adsorption, filtration, precipitation, and ion exchange. Finally, this review denoted biological nutrient removal, struvite precipitation, and breakpoint chlorination as the most effective and promising technologies for the removal of ammonia from aquatic environments, although at the expense of energy and operational cost. Lastly, the future perspective, avenues of exploitation, and technical facets that deserve in-depth exploration are duly underscored.

Primary and digested sludge-derived char as a Cd sorbent: feasibility of local utilisation

Cadmium (Cd) is a highly toxic metal, occurring in municipal wastewater and stormwater as well as in wastewater from various industries. Char derived from the pyrolysis of municipal sewage sludge has the potential to be a low-cost sorption media for the removal of Cd. However, the balance between possible local char production and demand has not been assessed previously. In this study, the Cd sorption capacities of chars derived from primary (PSC) and secondary sludge (DSC), as well as the feasibility of char production for Cd sorbent purposes, and the pyrolysis energy balance were evaluated. Results showed that the sorption capacity of PSC (9.1 mg/g; 800 °C, 70 min) was superior to that of DSC (6.0 mg/g; 800 °C, 70 min), and increased with a higher pyrolysis temperature. Pyrolysis of primary sludge had a more favourable energy balance compared with the pyrolysis of digested sludge; however, when accounting for loss of biogas production the energy balance of primary sludge pyrolysis was negative. Assessment of the regional demand (Västerås, Sweden) indicated that PSC or DSC may cover the local Cd sorbent demand. However, it was estimated that large char volumes would be required, thus making the use of DSC/PSC less feasible.

An Overview to Technical Solutions for Molybdenum Removal: Perspective from the Analysis of the Scientific Literature on Molybdenum and Drinking Water (1990–2019)

A bibliometric analysis using the Scopus database was performed to investigate the research documents published from 1990 to 2019 in scientific sources related to molybdenum in drinking water and determine the quantitative characteristics of the research in this period. The results from the analysis revealed that the number of publications was maintained at a regular production of around 5 papers per year until 2009, followed by a fast linear increase in the production in the period from 2010 to 2016 (29 papers in 2016), but the scientific production regarding this topic was reduced in 2017 and 2018 to recover the production obtained in 2016 once again in 2019. The total contribution of the three most productive countries (USA, China and India, respectively) accounted for around 50% of the total number of publications. Environmental Science was the most common subject (51.4% contribution), followed by Chemistry (26.7% contribution). The research efforts targeted toward the search for technical solutions for molybdenum removal from water are not as important as the ones focused on the identification of molybdenum-polluted water bodies and the analysis of the health effects of the intake of molybdenum. Nevertheless, examples of technological treatments to remove molybdenum from the aqueous solution include the use of adsorption and ion exchange; coagulation, flocculation and precipitation followed by filtration; membrane technologies and biological treatments.

Comparative Life Cycle Assessment of two advanced treatment steps for wastewater micropollutants: How to determine whole-system environmental benefits?

Advanced wastewater treatment (AWT) technologies are now considered to target urban micropollutants (MPs) before discharge into receiving water bodies and to comply with specific criteria for reuse. Extra energy and/or resources are necessary to achieve the elimination of MPs. Using the Life Cycle Assessment framework, this study assesses net environmental efficiencies for two AWTs (i) ozone systems (air-fed and pure oxygen-fed) and (ii) granular activated carbon filter. Sixty-five MPs with proven removal efficiency values and toxicity and/or ecotoxicity potentials were included in this study building on results from recent research. Consolidated Life Cycle Inventories with data quality and uncertainty characterization were produced with an emphasis on operational inputs. Results show that the direct water quality benefits obtained from AWT are outweighed by greater increases in indirect impacts from energy and resource demands. Future research should include water quality aspects not currently captured in life cycle impact assessment, such as endocrine disruption and whole-effluent toxicity, in order to assess the complete policy implications of MP removal strategies.

Antimony from brake dust to the combined sewer collection system via road effluent under rainy conditions

Abrasion of the brake lining of automobiles is one of the main antimony (Sb) sources on the road. Therefore, the road effluent possibly supplies Sb to the combined sewer collection system. However, Sb in road-sewer systems has attracted little concern, although heavy metals such as copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in sewer water have been studied by many previous authors. We investigated the effect of road effluent on Sb in the combined sewer water by collecting road effluent, road dust, and sewer water under rainy and dry weather conditions. Sb in road effluent showed a significantly higher concentration than the other types of samples, and the Sb concentration in sewer during wet weather was significantly higher than that during dry weather. Furthermore, the Sb concentration in sewer water decreased with time during a wash-off event. Clear positive relationships between Sb and Cu and between Sb and Ba in both road effluent and road dust extract indicate the effect of brake abrasion because the brake lining contains Cu, Sb, and Ba in high concentrations. Approximately 42% of Sb load occurred during the wash-off event, while the loads of Cu and Ba were much less. Unlike Cu and Ba, we conclude that Sb in combined sewer water largely depends on road effluent in wet weather due to the wash-off of road dust, which is probably associated with brake lining abrasion.

Removal of Heavy Metals during Primary Treatment of Municipal Wastewater and Possibilities of Enhanced Removal: A Review

Resource reuse has become an important aspect of wastewater management. At present, use of sludge in agriculture is one of the major reuse routes. Conventional municipal wastewater treatment does not involve any designated process for removal of heavy metals, and these distribute mainly between effluent and sludge. Enhanced removal of heavy metals during primary treatment may decrease the heavy metal concentrations in both effluent and sludge from secondary treatment and promote long-term reuse of secondary sludge. This review considers heavy metal occurrence and removal during primary settling, together with possible treatment technologies for heavy metal removal in primary settlers and their theoretical performance. The variation in total heavy metal concentrations and dissolved fraction in raw municipal wastewater points to a need for site-specific assessments of appropriate technologies for improved heavy metal removal. Studies examining the heavy metal speciation beyond dissolved/particulate are few. Missing or disparate information on process parameters such as hydraulic retention time, pH and composition of return flows makes it hard to generalize the findings from studies concerning heavy metal removal in primary settlers. Coagulation/flocculation and use of low-cost sorbents were identified as the most promising methods for enhancing heavy metal removal during primary settling. Based on the available data on heavy metal speciation and removal during primary settling, sorption technologies may be most effective for enhancing the removal of Cu and Ni, while coagulation may be efficient for Cd, Cr, Cu, Pb, Zn and Hg removal (but not as efficient for Ni removal).

Improving the efficiency of wastewater treatment plants: Bio-removal of heavy-metals and pharmaceuticals by Azolla filiculoides and Lemna minuta

In this study, we investigated the removal of Fe(III), Cr(VI), Al(III), diclofenac, and levofloxacin from treated wastewater in the presence of the free-floating plants Azolla filiculoides and Lemna minuta, to understand whether these species can be effectively used in a surface flow constructed wetland as wastewater refining treatment. Fe and Al were selected owing to their wide use as coagulant agents in wastewater treatment plants for promoting clariflocculation processes, whilst Cr was chosen due to its common use in industry. Diclofenac and levofloxacin, two molecules belonging to the most widely used pharmaceutical classes in the world, were studied as representative anti-inflammatory drugs and antibiotics, respectively. The study was performed at laboratory scale, exposing the plants separately to each individual contaminant at the concentrations of 5 mg L^-1 for the metals (i.e. 2.5-5 times higher than the European limits concerning discharge into surface water), and 1 μg L^-1 for the pharmaceuticals (concentration levels commonly found in wastewater). Depending on the plant species and contaminant tested, the range of different effects observed included low toxicity (i.e. Cr, Fe and diclofenac in L. minuta) and even a stimulatory effect on plant growth (i.e. for A. filiculoides with Al and for L. minuta with Al and levofloxacin). Moreover, both species proved to be very effective in the removal of Fe, Al and levofloxacin, with A. filiculoides showing the best performance (removal efficiency of 92%, 96%, and 60%, respectively), whereas for Cr and diclofenac the removal was always less than 10%. The higher removal capacity of A. filiculoides compared to L. minuta can be attributed to its superior tolerance of the contaminants, probably in turn related to the presence of nitrogen-fixing microorganism in its fronds.

Monitoring and modelling of influent patterns, phase distribution and removal of 20 elements in two primary wastewater treatment plants in Norway

Many small- or medium-sized communities in Northern Europe employ only primary wastewater treatment plants (WWTPs) and effluent discharges can be a relevant source of pollution. The current study combines monitoring and modelling approaches to investigate concentrations, influent patterns, size distribution and removal of 20 elements for the two primary WWTPs (Ladehammeren, LARA; Høvringen, HØRA) serving Trondheim, the third largest city in Norway. Element concentrations were determined in raw influent wastewater, effluents and biosolids, and diurnal inflow patterns were assessed. The elemental distribution in particulate, colloidal and dissolved fractions of untreated wastewater was characterized using filtration separation and electron microscopy. An influent generator model and multivariate statistical analyses were used to determine release patterns and to predict the (co-)occurrence of selected elements. Raw influent wastewater concentrations for most elements were similar in the two WWTPs, with only Ca, Mn, Fe, Co and Ba being significantly higher (p < 0.05) in HØRA (which receives more household and hospital discharges). Removal efficiencies varied between elements, but in most cases reflected their association with particulates. Nanosized particles of several elements were detected, with Cu/Zn being most common. Measured concentrations of most elements followed typical diurnal wastewater discharge patterns and enrichment factors calculated for biosolids confirmed the importance of anthropogenic sources for P, Cu, Zn, Cd, As, Cr, Ni, Pb, V, Co and Fe. Elemental concentrations generally correlated well with total suspended solid (TSS) concentrations at HØRA, while this was less pronounced in LARA (possibly due to higher industrial contributions). In one of its first applications for WWTP influent pattern examination, principal component analysis was found to be instrumental for source identification of target elements, showing significant differences between LARA and HØRA influents. The combined experimental, statistical and modelling approaches used herein allowed for improved understanding of element sources, patterns of discharge and fate in primary WWTPs.

Occurrence and Fate of Heavy Metals in Municipal Wastewater in Heilongjiang Province, China: A Monthly Reconnaissance from 2015 to 2017

As one of the major sources of pollutions in the environments, effluents from municipal wastewater recently became a hot topic. This study quantified monthly county-level releases of five heavy metals, i.e., lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg), from municipal wastewater into the environment in the Heilongjiang Province of China, based on sampling, measurement, and modeling tools. Wastewater samples were collected from 27 municipal wastewater treatment plants (MWTPs) in 15 county-level cities of Heilongjiang every month from 2015 to 2017. The concentrations of five heavy metals were analyzed in both influents (Pb: 160 ± 100 μg/L; Cd: 15 ± 9.0 μg/L; Cr: 170 ± 64 μg/L; Hg: 0.67 ± 1.5 μg/L; As: 6.2 ± 4.8 μg/L) and effluents (Pb: 45 ± 15 μg/L; Cd: 5.2 ± 5.1 μg/L; Cr: 57 ± 13 μg/L; Hg: 0.28 ± 0.12 μg/L; As: 2.6 ± 1.4 μg/L). The removal ratios of the five heavy metals ranged from 50% to 67%. Inflow fluxes of Pb, Cr, and Cd displayed increasing trends first then decreased after reaching a maximum value, whereas those of Hg and Pb remained stable. Material flow analysis reveals that constructions of MWTPs are conducive to significantly reduce the releases of heavy metals from urban areas into the aquatic environment in the study area. Additionally, municipal wastewater sludge (used as fertilizer or spread on the land) could be a significant source of heavy metals in the land.

Population mobility and urban wastewater dynamics

Dynamic influent models, which have been proposed to test control strategies using virtual wastewater treatment plants, should be as realistic as possible. The number of inhabitants in the catchment at any given time and their ways of life are among the parameters affecting the quality of these models. Census data related to work and school commutes were used to evaluate the number of people present in a given urban area. Based on the example of a large urban catchment (Grand Nancy, France), the results show that a population increase of 30% could occur during working hours resulting from the imbalance between workers leaving and coming into the catchment. Combined with information related to the local way of life, variation in the population helps to explain changes in wastewater flow rate and pollution (carbon, nitrogen, phosphorus and heavy metals), which present several maxima reflecting daily activities, such as bladder voiding, meals, the use of washrooms, etc. However, no well-defined variation patterns for pH and conductivity, which are linked to the concentrations of anions and cations in the wastewater, were observed. Slight reductions (up to 10% on Sundays) in the flow and pollution load were observed on weekends as the commuter flow decreased. Census data proved to be efficient in helping to understand the daily pattern of urban wastewater characteristics.

Impacts of coagulation-flocculation treatment on the size distribution and bioavailability of trace metals (Cu, Pb, Ni, Zn) in municipal wastewater

This study investigated the impact of coagulation-flocculation treatment on metal form and bioavailability in municipal wastewater. Real humus effluent samples were separated into particulate, colloidal and truly dissolved fractions before and after treatment with either ferric chloride (FeCl₃) or the biopolymer Floculan. Results revealed that both reagents effectively (≥48%) eliminated Cu, Pb and Zn from the particulate fraction and removed Cu and Zn from the colloidal fraction in conjunction with colloidal organic carbon (COC). Although organics in the truly dissolved fraction were resistant to removal, Floculan reduced Cu in this fraction by 72% owing to the complexation of free Cu ions to phenol and amino groups along the polymeric chains, revealing an additional removal pathway. In fact, COC removed in the CF process by Floculan was replaced with truly dissolved compounds, input as a result of this reagents organic composition. Floculan, therefore, reduced the soluble concentration of Cu and Zn without changing the DOC concentration, thus reducing the bioavailability of these metals in treated effluent. FeCl₃ did not reduce the bioavailability of target metals, thus did not deliver any environmental benefit. This work provides important information for the selection and development of high performance coagulants to improve metal removal.

Distribution of trace metals (Cu, Pb, Ni, Zn) between particulate, colloidal and truly dissolved fractions in wastewater treatment

The distribution of Cu, Pb, Ni and Zn between particulate, colloidal and truly dissolved size fractions in wastewater from a trickling filter treatment plant was investigated. Samples of influent, primary effluent, humus effluent, final effluent and sludge holding tank returns were collected and separated into particulate (i.e. > 0.45 μm), colloidal (i.e. 1 kDa to 0.45 μm), and truly dissolved (i.e. < 1 kDa) fractions using membrane filters. In the influent, substantial proportions of Cu (60%), Pb (67%), and Zn (32%) were present in the particulate fraction which was removed in conjunction with suspended particles at the works in subsequent treatment stages. In final effluent, sizeable proportions of Cu (52%), Pb (32%), Ni (44%) and Zn (68%) were found within the colloidal size fraction. Calculated ratios of soluble metal to organic carbon suggest the metal to be adsorbed to or complexed with non-humic macromolecules typically found within the colloidal size range. These findings suggest that technologies capable of removing particles within the colloidal fraction have good potential to enhance metals removal from wastewater.

Mercury and antimony in wastewater: fate and treatment

It is important to understand the fate of Hg and Sb within the wastewater treatment process so as to examine potential treatment options and to ensure compliance with regulatory standards. The fate of Hg and Sb was investigated for an activated sludge process treatment works in the UK. Relatively high crude values (Hg 0.092 μg/L, Sb 1.73 μg/L) were observed at the works, whilst low removal rates within the primary (Hg 52.2 %, Sb 16.3 %) and secondary treatment stages (Hg 29.5 %, Sb -28.9 %) resulted in final effluent concentrations of 0.031 μg/L for Hg and 2.04 μg/L for Sb. Removal of Hg was positively correlated with suspended solids (SS) and chemical oxygen demand (COD) removal, whilst Sb was negatively correlated. Elevated final effluent Sb concentrations compared with crude values were postulated and were suggested to result from Sb present in returned sludge liquors. Kepner Tregoe (KT) analysis was applied to identify suitable treatment technologies. For Hg, chemical techniques (specifically precipitation) were found to be the most suitable whilst for Sb, adsorption (using granulated ferric hydroxide) was deemed most appropriate. Operational solutions, such as lengthening hydraulic retention time, and treatment technologies deployed on sludge liquors were also reviewed but were not feasible for implementation at the works.

Lab-scale experimental strategy for determining micropollutant partition coefficient and biodegradation constants in activated sludge

The nitrifying/denitrifying activated sludge process removes several micropollutants from wastewater by sorption onto sludge and/or biodegradation. The objective of this paper is to propose and evaluate a lab-scale experimental strategy for the determination of partition coefficient and biodegradation constant for micropollutant with an objective of modelling their removal. Four pharmaceutical compounds (ibuprofen, atenolol, diclofenac and fluoxetine) covering a wide hydrophobicity range (log Kow from 0.16 to 4.51) were chosen. Dissolved and particulate concentrations were monitored for 4 days, inside two reactors working under aerobic and anoxic conditions, and under different substrate feed conditions (biodegradable carbon and nitrogen). We determined the mechanisms responsible for the removal of the target compounds: (i) ibuprofen was biodegraded, mainly under aerobic conditions by cometabolism with biodegradable carbon, whereas anoxic conditions suppressed biodegradation; (ii) atenolol was biodegraded under both aerobic and anoxic conditions (with a higher biodegradation rate under aerobic conditions), and cometabolism with biodegradable carbon was the main mechanism; (iii) diclofenac and fluoxetine were removed by sorption only. Finally, the abilities of our strategy were evaluated by testing the suitability of the parameters for simulating effluent concentrations and removal efficiency at a full-scale plant.