Treatment of micropollutants in wastewater: Balancing effectiveness, costs and implications.

In this contribution, we analyse scenarios of advanced wastewater treatment for the removal of micropollutants. By this we refer to current mainstream, broad spectrum processes including ozonation and sorption onto activated carbon. We argue that advanced treatment requires properly implemented tertiary (nutrient removal) treatment in order to be effective. We review the critical aspects of the main advanced treatment options, their advantages and disadvantages. We propose a quantification of the costs of implementing advanced treatment, as well as upgrading plants from secondary to tertiary treatment when needed, and we illustrate what drives the costs of advanced treatment for a set of standard configurations. We propose a cost function to represent the total costs (investment, operation and maintenance) of advanced treatment. We quantify the implications of advanced treatment in terms of greenhouse gas emissions. Based on the indicators of total toxic discharge, toxicity at the discharge points and toxicity across the stream network discussed in Pistocchi et al. (2022), we compare costs and effectiveness of different scenarios of advanced treatment. In principle the total toxic load and toxicity at the points of discharge could be reduced by about 75 % if advanced treatment processes were implemented virtually at all wastewater treatment plants, but this would entail costs of about 4 billion euro/year for the European Union as a whole. We consider a "compromise" scenario where advanced treatment is required at plants of 100 thousand population equivalents (PE) or larger, or at plants between 10 and 100 thousand PE if the dilution ratio at the discharge point is 10 or less. Under this scenario, the length of the stream network exposed to high toxicity would not increase significantly compared to the previous scenario, and the other indicators would not deteriorate significantly, while the costs would remain at about 1.5 billion Euro/year. Arguably, costs could be further reduced, without a worsening of water quality, if we replace a local risk assessment to generic criteria of plant capacity and dilution in order to determine if a WWTP requires advanced treatment.

Analysis of the variation of costs for sewage sludge transport, recovery and disposal in Northern Italy: a recent survey (2015-2021).

The cost for the recovery/disposal of residues produced by wastewater treatment plants (WWTPs) represents a relevant aspect in the economics of WWTP management. We elaborated and applied a desk-based methodology to analyze tender processes and to investigate quantitatively and qualitatively the variability of unit costs for sewage sludge (EWC 190805) management in Northern Italy from 2015 to 2021. We conducted a qualitative survey for operators of the sector. Unit costs for sludge management increased over time. The unit cost was mostly affected by the type of sludge recovery/disposal being the cost for recovery in agriculture (direct or by composting) lower than incineration and landfilling. Other variables influencing the cost were the distance and discount offered by the contractor. Regulatory and judiciary events determined a sudden increase of sludge disposal costs in Italy between 2017 and 2019. Recovery in agriculture, when practicable, remains the preferable option. Results can orient and support the optimization of sludge management costs and be of interest for future studies at national or European level.

Interpreting per capita loads of organic matter and nutrients in municipal wastewater: A study on 168 Italian agglomerations.

The size of an agglomeration is expressed in population equivalent, referring to the maximum average weekly load during the year according to the European Directive 271/91. This quantity, multiplied by the daily biochemical oxygen demand (BOD) produced by one population equivalent (which is 60 g d-1 PE-1, by definition), yields the design biodegradable organic load of the wastewater treatment plant. The same agglomeration size is compared against the capacity of the wastewater treatment plant (WWTP) for plant conformity verification by the European Commission. However, field observations show remarkable fluctuations of the daily mass flows entering a WWTP, often considerably below or above the expected load calculated according to the Directive prescriptions. A wrong estimation of the real influent load adversely affects the plant design and operation, and may lead to a misleading verification of its conformity to the agglomeration. In this work, a statistical data analysis on 168 agglomerations was performed, aiming at verifying the consistency between the expected loads of BOD, chemical oxygen demand (COD), nitrogen and phosphorus and the mass flows measured at the treatment plant inlet. Only 30-40% of the total analysed cases were found having an actual load compatible with the expected one. In these cases, the average per capita daily loads of BOD, COD, nitrogen and phosphorus, calculated over 2-3 years data pools, resulted: 44.6 ± 5.9, 82.4 ± 11, 9.4 ± 1.1, and 1.08 ± 0.13 g d-1, respectively, while the daily BOD per capita production of 60 g represented a value in between the 70th and the 90th percentiles of the actual daily load distributions. For the remaining 60-70% of the total cases, variably-remarkable positive or negative discrepancies between the nominal pollutant loads generated by the agglomeration and those measured at the plant inlet could be detected and possible causes were pointed out.

Reducing energy demand by the combined application of advanced control strategies in a full scale WWTP.

Two advanced control strategies were applied in the secondary and tertiary stages, respectively, of a full scale wastewater treatment plant (WWTP). This has a nominal capacity of 330,000 population equivalent (PE), a complex configuration (having been upgraded several times through the years), and it faces significant seasonal load fluctuations (being located in a touristic area, in Northern Italy). The lifting station of the tertiary treatments (devoted to phosphorus precipitation and UV disinfection) was optimized by adjusting the pumped flowrate, depending on influent phosphorus concentration. A preliminary simulation showed that a 15% reduction of pumping energy could be achieved. This result was confirmed by field measurements. Moreover, a fuzzy control system was designed and applied to one of the six parallel nitrification reactors, yielding a reduction of more than 25% of the power requirement for aeration. Overall, the combined application of the two controllers led to a 7% reduction of the total energy consumption of the plant. This result is particularly promising given that the fuzzy controller was applied only to one of six biological reactors.

Energy saving for air supply in a real WWTP: application of a fuzzy logic controller.

An unconventional cascade control system, for the regulation of air supply in activated sludge wastewater treatment plants (WWTPs), was tested. The dissolved oxygen (DO) set point in the aeration tank was dynamically calculated based on effluent ammonia concentration, following a fuzzy logic based approach. First, simulations were conducted, according to the BSM2 protocol, for a general comparison with more conventional control strategies. It turned out that the effluent quality could be improved by 7-8%, based on the EQI parameter. Moreover, the aeration energy requirement could be reduced up to 13%. Subsequently, the system was installed in a full-scale WWTP. While stably complying with the ammonia effluent standard (10 mg/L), excess air supply was prevented, and a reduction of the specific power consumption (kWh/kgCODremoved) of 40-50% was recorded with respect to the previously installed PID controller (fixed DO set point).

Treatment of aqueous wastes by means of Thermophilic Aerobic Membrane Reactor (TAMR) and nanofiltration (NF): process auditing of a full-scale plant.

This work focuses on the Thermophilic Aerobic Membrane Reactor (TAMR) process. The research was carried out on a full-scale facility where, all along a 12-year period, daily monitoring and process audit tests were conducted for the process analysis and optimization. The plant treated -light and high-strength aqueous wastes and two different configurations were adopted: (1) thermophilic biological reactor + ultrafiltration (TAMR) and (2) TAMR + nanofiltration (TAMR + NF). In the latter case, the average chemical oxygen demand removal yield was equal to 89% and an effective denitrification (nitrogen oxides removal equal to 96%) was achieved by reducing the dissolved oxygen concentration in the bioreactor. Low specific sludge production was observed. Poor sludge settling properties were measured by a lab-scale settling test; respirometric tests (nitrogen uptake rate and ammonia uptake rate) showed the presence of denitrification and the inhibition of nitrification. Hydrodynamic tests revealed the presence of a significant dead space, thus showing room for improving the overall process performance. Finally, the rheological properties of the sludge were measured as a function of the biomass concentration, pH, temperature, and aeration scheme.

Techno-economic performance indicators of municipal solid waste collection strategies.

Several indicators for the evaluation of the MSW collection systems have been proposed in the literature. These evaluation tools consider only some of the aspects that influence the operational efficiency of the collection service. The aim of this paper is to suggest a set of (easy to calculate) indicators that overcomes this limitation, taking into account both the characteristics of collected waste and the operational - economic performance. The main components of the collection system (labour, vehicles and containers) are separately considered so that it is possible to quantify and compare their role within the whole process. As an example of application, the proposed approach was used for comparing the MSW collection strategies adopted in four towns in Northern Italy. Results are discussed and a comparison with alternative assessment methods available in the scientific literature is reported.

Is anaerobic digestion effective for the removal of organic micropollutants and biological activities from sewage sludge?

The occurrence of emerging organic micropollutants (OMPs) in sewage sludge has been widely reported; nevertheless, their fate during sludge treatment remains unclear. The objective of this work was to study the fate of OMPs during mesophilic and thermophilic anaerobic digestion (AD), the most common processes used for sludge stabilization, by using raw sewage sludge without spiking OMPs. Moreover, the results of analytical chemistry were complemented with biological assays in order to verify the possible adverse effects (estrogenic and genotoxic) on the environment and human health in view of an agricultural (re)use of digested sludge. Musk fragrances (AHTN, HHCB), ibuprofen (IBP) and triclosan (TCS) were the most abundant compounds detected in sewage sludge. In general, the efficiency of the AD process was not dependent on operational parameters but compound-specific: some OMPs were highly biotransformed (e.g. sulfamethoxazole and naproxen), while others were only slightly affected (e.g. IBP and TCS) or even unaltered (e.g. AHTN and HHCB). The MCF-7 assay evidenced that estrogenicity removal was driven by temperature. The Ames test did not show point mutation in Salmonella typhimurium while the Comet test exhibited a genotoxic effect on human leukocytes attenuated by AD. This study highlights the importance of combining chemical analysis and biological activities in order to establish appropriate operational strategies for a safer disposal of sewage sludge. Actually, it was demonstrated that temperature has an insignificant effect on the disappearance of the parent compounds while it is crucial to decrease estrogenicity.

High-strength wastewater treatment in a pure oxygen thermophilic process: 11-year operation and monitoring of different plant configurations.

This research was carried out on a full-scale pure oxygen thermophilic plant, operated and monitored throughout a period of 11 years. The plant treats 60,000 t y⁻¹ (year 2013) of high-strength industrial wastewaters deriving mainly from pharmaceuticals and detergents production and landfill leachate. Three different plant configurations were consecutively adopted: (1) biological reactor + final clarifier and sludge recirculation (2002-2005); (2) biological reactor + ultrafiltration: membrane biological reactor (MBR) (2006); and (3) MBR + nanofiltration (since 2007). Progressive plant upgrading yielded a performance improvement chemical oxygen demand (COD) removal efficiency was enhanced by 17% and 12% after the first and second plant modification, respectively. Moreover, COD abatement efficiency exhibited a greater stability, notwithstanding high variability of the influent load. In addition, the following relevant outcomes appeared from the plant monitoring (present configuration): up to 96% removal of nitrate and nitrite, due to denitrification; low-specific biomass production (0.092 kgVSS kgCODremoved⁻¹), and biological treatability of residual COD under mesophilic conditions (BOD5/COD ratio = 0.25-0.50), thus showing the complementarity of the two biological processes.

Mass and energy balances of sludge processing in reference and upgraded wastewater treatment plants.

This paper describes the preliminary assessment of a platform of innovative upgrading solutions aimed at improving sludge management and resource recovery in wastewater treatment plants. The effectiveness of the upgrading solutions and the impacts of their integration in model reference plants have been evaluated by means of mass and energy balances on the whole treatment plant. Attention has been also paid to the fate of nitrogen and phosphorus in sludge processing and to their recycle back to the water line. Most of the upgrading options resulted in reduced production of dewatered sludge, which decreased from 45 to 56 g SS/(PE × day) in reference plants to 14-49 g SS/(PE × day) in the upgraded ones, with reduction up to 79% when wet oxidation was applied to the whole sludge production. The innovative upgrades generally entail an increased demand of electric energy from the grid, but energy recovery from biogas allowed to minimize the net energy consumption below 10 kWh/(PE × year) in the two most efficient solutions. In all other cases the net energy consumption was in the range of -11% and +28% of the reference scenarios.

Treatment of high strength pharmaceutical wastewaters in a Thermophilic Aerobic Membrane Reactor (TAMR).

In the present work we studied the thermophilic biological treatability of high strength liquid wastes from a pharmaceutical industry (rich in organic matter - COD: Chemical Oxygen Demand, nutrients and salinity). Different mixtures (with concentrations of COD, phosphorus and chloride up to 57,000 mg L(-1), 2000 mg L(-1) and 9000 mg L(-1), respectively) were tested. The pilot plant used in this work was designed and built with dimensions comparable to a semi-industrial unit. The results are therefore representative for full-scale applications. During four months of experimentation, the pilot plant (TAMR - Thermophilic Aerobic Membrane Reactor) was operated at 49 ± 1 °C and the organic loading rate was 1.5-5.5 kgCOD m(-3) d(-1) with a hydraulic retention time of 5-10 days. Main results are the following: a) extremely high COD removal rate (up to 98%); b) very low sludge production (∼0.016 kgVSS produced kgCOD removed(-1)); c) suitability as a pre-treatment to a conventional (e.g. activated sludge) biological treatment (the studied pharmaceutical industrial wastewaters are discharged into the sewer system for final polishing in a centralized municipal wastewater treatment plant) and d) high phosphorus removal (up to 99%).

Tertiary ozonation of industrial wastewater for the removal of estrogenic compounds (NP and BPA): a full-scale case study.

Wastewater treatment plant (WWTP) effluents are considered to be a major source for the release in the aquatic environment of endocrine-disrupting compounds (EDCs). Ozone has proved to be a suitable solution for polishing secondary domestic effluents. In this work, the performance of a full-scale ozonation plant was investigated in order to assess the removal efficiency of four target EDCs: nonylphenol, nonylphenol monoethoxylate, nonylphenol diethoxylate and bisphenol A. The studied system was the tertiary treatment stage of a municipal WWTP which receives an important industrial (textile) load. Chemical analyses showed that the considered substances occurred with a significant variability, typical of real wastewaters; based on this, ozonation performance was carefully evaluated and it appeared to be negatively affected by flow-rate increase (during rainy days, with consequent contact time reduction). Moreover, EDCs' measured removal efficiency was lower than what could be predicted based on literature data, because of the relatively high residual content of biorefractory compounds still present after biological treatment.

How green are environmental technologies? A new approach for a global evaluation: the case of WWTP effluents ozonation.

The research on the impact of chemical pollution is now increasingly attracted by the topic of organic micropollutants: as secondary biological treatment of wastewater does not provide the complete elimination of these substances, an advanced treatment downstream the biological process can be implemented. Notwithstanding, the benefits of improved effluent quality can be weakened by the negative effects on air quality, when energy consumption and related pollutants emissions deriving from the advanced treatment technologies are taken into account. It is the aim of this work to present an innovative methodology to judge the environmental compatibility of wastewater treatment processes on the basis of the damage on human health produced/avoided, expressed as an economic value. In particular, while for air pollution the established external costs were applied, for water pollution the rates of the impacts on human health have been evaluated in terms of Global Burden of Disease and measured in units of DALY (Disability-Adjusted Life Years), then converted into costs based on Gross Domestic Product. As a first application, this procedure was used for assessing environmental compatibility of a final ozonation: the results of this study showed that the reduction of water pollution achieved by means of ozonation might be beneficial for human health at an extent which is in the same order of magnitude of damage caused by air pollution, emphasizing that the question if the use of advanced (energy-intensive) treatments is a proper solution to remove organic micropollutants from wastewater remains still open.

EDCs, estrogenicity and genotoxicity reduction in a mixed (domestic + textile) secondary effluent by means of ozonation: a full-scale experience.

WWTP (wastewater treatment plant) effluents are considered to be a major source for the release in the aquatic environment of EDCs (Endocrine-Disrupting Compounds), a group of anthropogenic substances able to alter the normal function of the endocrine system. The application of conventional processes (e.g. activated sludge with biological nitrogen removal) does not provide complete elimination of all these micropollutants and, consequently, an advanced treatment should be implemented. This experimental work was conducted on the tertiary ozonation stage of a 140,000 p.e. activated sludge WWTP, treating a mixed domestic and textile wastewater: an integrated monitoring, including both chemical (nonylphenol, together with the parent compounds mono- and di-ethoxylated, and bisphenol A were chosen as model EDCs) and biological (estrogenic and genotoxic activities) analyses, was carried out. Removal efficiencies of measured EDCs varied from 20% to 70%, depending on flow conditions (ozone dosage being 0.5 gO3/gTOC). Biological tests, furthermore, displayed that the oxidation stage did not significantly reduce (only by 20%) the estrogenicity of the effluent and revealed the presence and/or formation of genotoxic compounds. These results highlight the importance of the application of an integrated (biological+chemical) analytical procedure for a global evaluation of treatment suitability; poor performances recorded in this study have been attributed to the presence of a significant industrial component in the influent wastewater.

Removal of endocrine disrupting compounds from wastewater treatment plant effluents by means of advanced oxidation.

Municipal sewage and WWTP effluents are considered to be a major source of pollution, regarding the occurrence of endocrine disrupting compounds (EDCs) in the environment. Although removal potential of many EDCs by conventional WWTPs is recognised, literature data are not easily comparable. Besides, in order to reach very low concentrations, a further treatment might be sometimes required. Positive results can be achieved by tertiary chemical oxidation; nevertheless, technical-economic suitability is still to be fully demonstrated. In this work, two estrogen-like susbstances were considered: nonylphenol (NP) (and its parent compounds) and bisphenol A (BPA). The experimental work was conducted at Verona (Northern Italy) WWTP (370,000 p.e.): after a 15 days sampling campaign, which was carried out in order to calculate mass balance of target compounds, chemical oxidation tests were performed on effluent by means of UV/H(2)O(2) process and ozonation. Technical-economic feasibility of these solutions is discussed.

Integration between chemical oxidation and membrane thermophilic biological process.

Full scale applications of activated sludge thermophilic aerobic process for treatment of liquid wastes are rare. This experimental work was carried out at a facility, where a thermophilic reactor (1,000 m(3) volume) is operated. In order to improve the global performance of the plant, it was decided to upgrade it, by means of two membrane filtration units (ultrafiltration -UF-, in place of the final sedimentation, and nanofiltration -NF-). Subsequently, the integration with chemical oxidation (O(3) and H(2)O(2)/UV processes) was taken into consideration. Studied solutions dealt with oxidation of both the NF effluents (permeate and concentrate). Based on experimental results and economic evaluation, an algorithm was proposed for defining limits of convenience of this process.

Process improvement and energy saving in a full scale wastewater treatment plant: air supply regulation by a fuzzy logic system.

Achieving good performance in air supply control is an important goal in the management of wastewater treatment plants, whose highly nonlinear behaviour makes the application of conventional control techniques problematic. This paper presents the development and experimentation of a fuzzy logic system for air supply regulation in a full scale municipal wastewater treatment plant. The system is composed of two main modules, one devoted to continuously adjusting the DO set point on the basis of the current effluent NH4(+)-N concentration (on-line measurement), and the other devoted to achieve the DO set point by controlling air supply devices. The experiment was carried out on the plant for about one year, leading to significant advantages in terms of both process stability and energy saving.

How to assess chemical oxidation efficiency.

In this work, a real wastewater (deriving from the chemical-pharmaceutical field) was treated by means of H2O2/UV process under different conditions in a pilot-scale plant. Several methods were used in order to assess the oxidation efficiency and to understand the main reaction features. It was shown that non-conventional COD measurement (with a 75 degrees C digestion of the sample) is helpful for understanding reaction mechanisms, when integrated with TOC and COD analyses and GC-MS determinations. For the biodegradability study, beside BOD (5 and 20 days) measurements, OUR and AUR tests provide additional information especially when wastewater is tested by taking the activated sludge from the treatment plant which should really be fed with it. Finally, dehydrogenase activity measurements can show the presence of complex organic matter, which may be degraded only by an acclimated biomass.

Field monitoring and evaluation of innovative solutions for cleaning storm water runoff.

Urbanization increases the variety and amount of pollutants transported to receiving waters. Sediment from development and new construction; oil, grease, and toxic chemicals from automobiles; nutrients and pesticides from turf management and gardening; viruses and bacteria from failing septic systems; road salts; and heavy metals are examples of pollutants generated in urban areas. Sediments and solids constitute the largest volume of pollutant loads to receiving waters in urban areas. When runoff enters storm drains, it carries many of these pollutants with it. In older cities, this polluted runoff is often released directly into open waterways without any treatment. Increased pollutant loads can harm fish and wildlife populations, kill native vegetation, foul drinking water supplies, and make recreational areas unsafe. The objective of the study, performed by University of Pavia (Italy), University of Brescia (Italy) and GreenTechTexas International (US), reported herein is to evaluate the use of an innovative stormwater technology (EcoDräin) to reduce pollution due to urban runoff in existing urban areas. The paper describes the methodology and the results achieved with tests conducted in laboratory in Pavia University in Italy and in two pilot areas in Italy and in Australia to investigate the EcoDräin's effectiveness for oil and heavy metals retention and sediment trapping. In the tests performed in a marina near Sydney in Australia a reduction has been achieved in oil and grease concentration higher than 95% and a reduction in metal concentration (particularly Copper, Lead and Zinc) close to 98%. The paper also describes the methodology of the analysis on the absorbing material after its use and the consequent determination of the most efficient and environmentally safe way to dispose of consummated absorbent.

The role of chemical oxidation in combined chemical-physical and biological processes: experiences of industrial wastewater treatment.

In this work, some experiences are described concerning the application of chemical oxidation in the treatment of industrial wastewaters in combination with other chemical-physical and/or biological processes. In the first case, two different wastewaters from saturated and unsaturated polyester resin production were considered. In a second case, optimal process conditions were assessed for the treatment of a wastewater deriving from polystyrene production. A third experience dealt with a comparison among different processes (flocculation, Fenton process, ozonisation, oxidation by means of ozone and hydrogen peroxide, oxidation by means of hydrogen peroxide and UV radiation), for the pretreatment of two industrial wastewaters (the first one being produced in a textile factory, the second one coming from detergent manufacturing). The evaluation of different processes was carried out by means of laboratory scale tests, considering treatment efficiency (organic substance removal, changes in wastewater biodegradability) and parameters (chemicals and energy consumption, sludge production) which play an important role in cost determination.