Evaluating the potential impact of energy-efficient ammonia control on the carbon footprint of a full-scale wastewater treatment plant.

An assessment was performed for elucidating the possible impact of different aeration strategies on the carbon footprint of a full-scale wastewater treatment plant. Using a calibrated model, the impact of different aeration strategies was simulated. The ammonia controller tested showed its ability in ensuring effluent ammonia concentrations compliant with regulation along with significant savings on aeration energy, compared to fixed oxygen set point (DOsp) control strategies. At the same time, nitrous oxide emissions increased due to accumulation of nitrification intermediates. Nevertheless, when coupled with the carbon dioxide emissions due to electrical energy consumption for aeration, the overall carbon footprint was only marginally affected. Using the local average CO2 emission factor, ammonia control slightly reduced the carbon footprint with respect to the scenario where DOsp was fixed at 2 mg·L-1. Conversely, no significant change could be detected when compared against the scenarios where the DOsp was fixed. Overall, the actual impact of ammonia control on the carbon footprint compared to other aeration strategies was found to be strictly connected to the sources of energy employed, where the larger amount of low CO2-emitting energy is, the higher the relative increase in the carbon footprint will be.

The upgrading of conventional activated sludge processes with thermophilic aerobic membrane reactor: Alternative solutions for sludge reduction.

Sludge recovery/disposal represents one of the most crucial aspects related to the management of wastewater treatment plants. The most widely diffused technology for the treatment of industrial and municipal wastewaters is the conventional activated sludge (CAS) process, which is characterized by a relatively high excess sludge production. Different technical solutions are proposed in the literature for sludge minimization and they can be applied either on wastewater line (WL) or sludge line (SL). This work is focused on different approaches based on the use of Thermophilic Aerobic Membrane Reactor (TAMR): this can be added to a CAS plant, and integrated to WL or SL, yielding a significant sludge reduction. The process performance was analysed in terms of volatile solids (VS) reduction and specific sludge production. The TAMR was tested both at full-scale and pilot-scale with different feeding substrates: industrial wastewater for the full-scale plant; industrial wastewater, sludge and a mix of these for the pilot-scale plants. The results obtained are: (i) good solids removal (38-90% and 40-50% in terms of VS for sludge and mix of industrial wastewater and sludge, respectively), (ii) low specific sludge production (0.01-0.09 kgVSS produced kgCOD removed-1 for industrial wastewater and 0.014-0.069 kgVSS produced kgCOD removed-1 for mix of industrial wastewater and sludge) and (iii) a significant reduction of sludge when CAS is improved with the TAMR technology.

Promoting biological phosphorus removal in a full scale pre-denitrification wastewater treatment plant.

A survey conducted in Italy revealed that less than 0.5% out of a sample of over 2,000 municipal wastewater treatment plants is equipped with an enhanced biological phosphorus removal process. Conditions promoting biological phosphorus removal have been investigated by monitoring three real plants equipped with, respectively: (A) simultaneous chemical precipitation; (B) enhanced biological removal powered by chemical precipitation; (C) tertiary chemical precipitation with evidence of phosphate accumulating bacteria. An anaerobic compartment revealed essential for the growth of these microorganisms, the readily degradable organic concentration in the influent playing a minor role. Mapping dissolved oxygen and oxidation-reduction potential in different compartments of plant (C) was carried out to understand the reasons why phosphate accumulating bacteria were found even in the absence of anaerobic reactor. Finally, the possibility to exploit the biological phosphorus removal in plant (C), by adjusting the aeration conditions, was explored and an economic analysis showed this to be a preferable approach with respect to the chemical removal of phosphorus.

The role of bioassays in the evaluation of ecotoxicological aspects within the PEF/OEF protocols: The case of WWTPs.

The suitability evaluation of any industrial process should rely on economic, technical, social and, in particular, environmental aspects. The Commission Recommendation 2013/179/UE enables the improvement and the harmonization of the conventional evaluation of environmental footprints, such as LCA (Life Cycle Assessment), Carbon and Water Footprint, by suggesting the assessment of life cycle environmental performance of products and organisations (PEF, OEF). Novelty aspects reside in including new impact categories (namely, human toxicity cancer effects, human toxicity not-cancer effects and eco-toxicity). This paper presents an application of PEF/OEF protocol to the example case of an activated sludge wastewater treatment plant. Strengths and criticisms of this approach are discussed, by taking into consideration the possible final goal of the suitability assessment. Valuably, the adoption of bioassays (i.e., the input of their results in the models for calculating the life cycle environmental performance) for a more reliable evaluation of the impact on the ecosystem and human health is proposed.

Process auditing and performance improvement in a mixed wastewater-aqueous waste treatment plant.

The wastewater treatment process is based on complex chemical, physical and biological mechanisms that are closely interconnected. The efficiency of the system (which depends on compliance with national regulations on wastewater quality) can be achieved through the use of tools such as monitoring, that is the detection of parameters that allow the continuous interpretation of the current situation, and experimental tests, which allow the measurement of real performance (of a sector, a single treatment or equipment) and comparison with the following ones. Experimental tests have a particular relevance in the case of municipal wastewater treatment plants fed with a strong industrial component and especially in the case of plants authorized to treat aqueous waste. In this paper a case study is presented where the application of management tools such as careful monitoring and experimental tests led to the technical and economic optimization of the plant: the main results obtained were the reduction of sludge production (from 4,000 t/year w.w. (wet weight) to about 2,200 t/year w.w.) and operating costs (e.g. from 600,000 €/year down to about 350,000 €/year for reagents), the increase of resource recovery and the improvement of the overall process performance.

How far are we from closing the loop of sewage resource recovery? A real picture of municipal wastewater treatment plants in Italy.

This paper presents the results of a broad-scale survey of resource recovery implementation in Italian wastewater treatment plants (WWTPs). To the best of our knowledge, this is the first survey comprising a large number of WWTPs done in Europe: more than 600 plants were investigated, representing a treated load of around 20 million population equivalent (≈25% of the total in Italy). Conventional and innovative options for both material and energy recovery along the water and sludge line were surveyed, in order to i) offer a real and complete picture of the current state of resource recovery in WWTPs, and ii) underline key aspects and potential areas for improvements, as a baseline for future developments in the direction of more sustainable plants. Survey outcomes showed that resource recovery is just in its infancy in sewage treatment: only 40% of plants perform at least one option for material/energy recovery. The action most often implemented is recovery of material from surplus sludge for agricultural purposes and the internal reuse of treated effluent as water for various types of plant maintenance. The production of energy from biogas also occurs frequently but only in large plants. On the other hand, some well-known options, such as external reuse of treated effluent or nutrients recovery, were implemented only in a minority of plants: this is likely due to limitations resulting either from strict regulation or difficulty placing recovered products on the market. In conclusion, an overall explanation of these driving forces within the system is explored.

Treatment of high strength aqueous wastes in a thermophilic aerobic membrane reactor (TAMR): performance and resilience.

In the present work, the thermophilic aerobic membrane reactor technology was studied for the treatment of high strength aqueous wastes mainly containing dyes, surfactants and solvents. The thermophilic biomass resilience and the process stability under critical conditions (such as rapid rise of the mixed liquor pH, oxygen supply interruption, etc.) were also evaluated. The experimental work was carried out with the use of a pilot plant at semi-industrial scale, which was managed throughout for 14 months; the operation temperature was 49 °C and the organic loading rate was increased from 3 to 12 kgCOD m-3 d-1. Critical conditions, especially the interruption of oxygen supply, affected the pilot plant performance but did not cause a complete system break down. After the temporary reduction of process performance, also proven by the decrease in the oxygen consumption, the normal working conditions were restored. Moreover, the longer non-aerated phase involved a significant reduction (40%) of volatile suspended solids concentration in the biological reactor and the increase of 30% in foaming power; nevertheless, once the oxygen supply was reactivated, optimal conditions were rapidly restored. Therefore, the study showed the high resilience of the thermophilic biomass, which was able to recover full functionality after critical events.

Suitability of Sludge Biotic Index (SBI), Sludge Index (SI) and filamentous bacteria analysis for assessing activated sludge process performance: the case of piggery slaughterhouse wastewater.

Piggery slaughterhouse wastewater poses serious issues in terms of disposal feasibility and environmental impact, due to its huge organic load and variability. It is commonly treated by means of activated sludge processes, whose performance, in case of municipal wastewater, can be monitored by means of specific analyses, such as Sludge Biotic Index (SBI), Sludge Index (SI) and floc and filamentous bacteria observation. Therefore, this paper was aimed at assessing the applicability of these techniques to piggery slaughterhouse sewage. A plant located in Northern Italy was monitored for 1 year. Physical, chemical and operation parameters were measured; the activated sludge community (ciliates, flagellates, amoebae and small metazoa) was analysed for calculating SBI and SI. Floc and filamentous bacteria were examined and described accordingly with internationally adopted criteria. The results showed the full applicability of the studied techniques for optimizing the operation of a piggery slaughterhouse wastewater treatment plant.

Enhanced Versus Conventional Sludge Anaerobic Processes: Performances and Techno-Economic Assessment.

Sewage sludge processing is a key issue in water resource recovery facilities due to the inefficacy of conventional treatments to produce high quality biosolids to be safely used in agriculture. Under this framework, the performances of several enhanced stabilization processes, namely ultrasound-pretreated Mesophilic Anaerobic Digestion (US+MAD), thermophilic anaerobic digestion (TAD), thermal-pretreated TAD (TH+TAD) and ultrasound-pretreated inverse Temperature Phased Anaerobic Digestion (US+iTPAD) have been investigated. Such enhanced processes resulted in higher biogas yields and higher destruction of pathogens with respect to conventional MAD process, thus suggesting their feasibility in full-scale implementation perspectives. A procedure for technical-economic comparison of new sludge processing lines against conventional ones (benchmarking) was developed, based on the definition of technical issues (e.g. reliability, complexity, etc.) which are rated for each situation. Moreover, capital and operating costs were estimated. The enhanced processes analyzed in this work showed some potentially critical items, mainly related to energy balance and reagent consumption.

Treatment of sewage sludge in a thermophilic membrane reactor (TMR) with alternate aeration cycles.

The management of sewage sludge is becoming a more and more important issue, both at national and international level, in particular due to the uncertain recovery/disposal future options. Therefore, it is clear that the development of new technologies that can mitigate the problem at the source by reducing sludge production is necessary, such as the European Directive 2008/98/EC prescribes. This work shows the results obtained with a thermophilic membrane reactor, for processing a biological sludge derived from a wastewater treatment plant (WWTP) that treats urban and industrial wastewater. Sewage sludge was treated in a thermophilic membrane reactor (TMR), at pilot-scale (1 m(3) volume), with alternate aeration cycles. The experimentation was divided into two phases: a "startup phase" during which, starting with a psychrophilic/mesophilic biomass, thermophilic conditions were progressively reached, while feeding a highly biodegradable substrate; the obtained thermophilic biomass was then used, in the "regime phase", to digest biological sludge which was fed to the plant. Good removal yields were observed: 64% and 57% for volatile solids (VS) and total COD (CODtot), respectively, with an average hydraulic retention time (HRT) equal to 20 d, an organic loading rate (OLR) of about 1.4-1.8 kg COD m(-3) d(-1) and aeration/non aeration cycles alternated every 4 h.

Why use a thermophilic aerobic membrane reactor for the treatment of industrial wastewater/liquid waste?

This paper describes the advantages of thermophilic aerobic membrane reactor (TAMR) for the treatment of high strength wastewaters. The results were obtained from the monitoring of an industrial and a pilot scale plant. The average chemical oxygen demand (COD) removal yield was equal to 78% with an organic loading rate (OLR) up to 8-10 kgCOD m(-3) d(-1) despite significant scattering of the influent wastewater composition. Total phosphorus (TP) was removed with a rate of 90%, the most important removal mechanism being chemical precipitation (as hydroxyapatite, especially), which is improved by the continuous aeration that promotes phosphorus crystallization. Moreover, surfactants were removed with efficiency between 93% and 97%. Finally, the experimental work showed that thermophilic processes (TPPs) are complementary with respect to mesophilic treatments.

How can sludge dewatering devices be assessed? Development of a new DSS and its application to real case studies.

A key issue in biological Waste Water Treatment Plants (WWTPs) operation is represented by the sludge management. Mechanical dewatering is a crucial stage for sludge volume reduction; though, being a costly operation, its optimization is required. We developed an original experimental methodology to evaluate the technical (dewatering efficiency) and financial (total treatment costs) performance of dewatering devices, which might be used as a DSS (Decision Support System) for WWTP managers. This tool was then applied to two real case studies for comparing, respectively, three industrial size centrifuges, and two different operation modes of the same machine (fixed installation vs. outsourcing service). In both the cases, the best option was identified, based jointly on economic and (site-specific) technical evaluations.

Method for technical, economic and environmental assessment of advanced sludge processing routes.

The legislative framework in force in Europe entails restrictive effluent standards for sensitive areas, and quite severe restrictions on the properties of residual sewage sludge, both for landfill disposal and for agricultural use. Several technologies and management strategies have been proposed and applied in wastewater treatment plants to minimise sludge production and contamination. However, their techno-economic and environmental performance has to be carefully evaluated. The ROUTES project, funded within the EU Seventh Framework programme, aims to find new routes for wastewater treatment and sludge management and thereby guide EU members in their future choices. Within this project, the authors have developed and applied a procedure for techno-economic-environmental assessment of new wastewater and sludge processing lines in comparison to reference plants. The reference plants are model conventional plants that experience different types of problems and the new plants are modified plants in which different innovative technologies have been added to solve these problems. The procedure involves a rating of selected technical issues, estimates of operating costs and an assessment of environmental impacts from a life cycle perspective. This paper reports on the procedure and shows examples of results.

Plastics in biogenic matrices intended for reuse in agriculture and the potential contribution to soil accumulation.

The spread of biogenic matrices for agricultural purposes can lead to plastic input into soils, raising a question on possible consequences for the environment. Nonetheless, the current knowledge concerning the presence of plastics in biogenic matrices is very poor. Therefore, the objective of the present study was a quali-quantitative characterization of plastics in different matrices reused in agriculture as manures, digestate, compost and sewage sludges. Plastics were quantified and characterized using a Fourier Transform Infrared Spectroscopy coupled with an optical microscope (µFT-IR) in Attenuated Total Reflectance mode. Our study showed the presence of plastics in all the investigated samples, albeit with differences in the content among the matrices. We measured a lower presence in animal matrices (0.06-0.08 plastics/g wet weight w.w.), while 3.14-5.07 plastics/g w.w. were measured in sewage sludges. Fibres were the prevalent shape and plastic debris were mostly in the micrometric size. The most abundant polymers were polyester (PEST), polypropylene (PP) and polyethylene (PE). The worst case was observed in the compost sample, where 986 plastics/g w.w. were detected. The majority of these plastics were compostable and biodegradable, with only 8% consisting of fragments of PEST and PE. Our results highlighted the need to thoroughly evaluate the contribution of reused matrices in agriculture to the plastic accumulation in the soil system.

To spread or not to spread? Assessing the suitability of sewage sludge and other biogenic wastes for agriculture reuse.

Sewage sludge (biosolids) management represents a worldwide issue. Due to its valuable properties, approximately one half of the EU production is recovered in agriculture. Nevertheless, growing attention is given to potential negative effects deriving from the presence of harmful pollutants. It is recognized that a (even very detailed) chemical characterization is not able to predict ecotoxicity of a mixture. However, this can be directly measured by bioassays. Actually, the choice of the most suitable tests is still under debate. This paper presents a multilevel characterization protocol of sewage sludge and other organic residues, based on bioassays and chemical-physical-microbiological analyses. The detailed description of the experimental procedure includes all the involved steps: the criteria for selecting the organic matrices to be tested and compared; the sample pre-treatment required before the analyses execution; the chemical, physical and microbiological characterisation; the bioassays, grouped in three classes (baseline toxicity; specific mode of action; reactive mode of action); data processing. The novelty of this paper lies in the integrated use of advanced tools, and is based on three pillars:•the direct ecosafety assessment of the matrices to be reused.•the adoption of innovative bioassays and analytical procedures.•the original criteria for data normalization and processing.

Biodegradability, toxicity and mutagenicity of detergents: Integrated experimental evaluations.

The widespread use of detergents has raised concern with regard to the environmental pollution caused by their active ingredients, which are biorefractory, toxic and persistent. Since detergents are complex mixtures of different substances, in which synergistic effects may occur, we aimed to assess the mutagenicity of different detergent formulations, taking into account aquatic toxicity and ready biodegradability. We performed a ready biodegradability test (OECD 301 F), Daphnia magna and Vibrio fischeri toxicity tests, and mutagenicity tests (Salmonella/microsome test, Allium cepa test and comet assay). Six detergent formulations were examined, 3 pre-manufacture and 3 commercially available. All detergents presented ready biodegradability. EC50 values varied for all products, according to the marker organism used, but were always higher than the more stringent value considered for aquatic toxicity assessment (V. fischeri 10-60 mg/L; D. magna 25-300 mg/L; A. cepa 250-2000 mg/L). None of the detergents caused mutations in bacteria. However, one commercial ecolabelled product induced an increase in micronucleus frequency in A. cepa root cells. All pre-manufacture detergents and one commercial one, which gave negative results in the Ames and A. cepa tests, induced DNA damage in human leukocytes. A more accurate evaluation of the environmental impact of complex mixtures such as detergents requires a battery of tests to describe degradation, as well as toxicological and mutagenic features.

Improving the quality of wastewater treatment plant monitoring by adopting proper sampling strategies and data processing criteria.

Monitoring is a crucial operation for plant management. However, proper sampling procedures and data processing criteria are not always adopted. Wastewater treatment plants work under dynamic conditions, which poses a challenge for a correct performance assessment. The aim of this work is to analyse some important aspects of wastewater sampling and data processing, to identify case by case methods which should to be adopted in order to obtain reliable and consistent information on plant performance. The study was conducted through simulations and real data analyses. It turned out that: a) the preferable 24-hour composite sampling procedure is the flow-proportional mode; in addition, the required sampling frequency (i.e. the number of sub-samples to be taken to make the 24-h composite sample) increases as the percentage of population discontinuously discharging the monitored substance decreases; b) a Variability Index was defined to help find the minimum sampling frequency (i.e. the number of 24-h composite samples per year) for the calculation of annual mass flows with an acceptable uncertainty; and c) criteria were proposed for the identification of pseudo-steady state periods needed to calculate reliable mass balances and plant performance indicators.

Wastewater toxicity removal: Integrated chemical and effect-based monitoring of full-scale conventional activated sludge and membrane bioreactor plants.

The literature is currently lacking effect-based monitoring studies targeted at evaluating the performance of full-scale membrane bioreactor plants. In this research, a monitoring campaign was performed at a full-scale wastewater treatment facility with two parallel lines (traditional activated sludge and membrane bioreactor). Beside the standard parameters (COD, nitrogen, phosphorus, and metals), 6 polynuclear aromatic hydrocarbons, 29 insecticides, 2 herbicides, and 3 endocrine disrupting compounds were measured. A multi-tiered battery of bioassays complemented the investigation, targeting different toxic modes of action and employing various biological systems (uni/multicellular, prokaryotes/eukaryotes, trophic level occupation). A traffic light scoring approach was proposed to quickly visualize the impact of treatment on overall toxicity that occurred after the exposure to raw and concentrated wastewater. Analysis of the effluents of the CAS and MBR lines show very good performance of the two systems for removal of organic micropollutants and metals. The most noticeable differences between CAS and MBR occurred in the concentration of suspended solids; chemical analyses did not show major differences. On the other hand, bioassays demonstrated better performance for the MBR. Both treatment lines complied with the Italian law's "ecotoxicity standard for effluent discharge in surface water". Yet, residual biological activity was still detected, demonstrating the adequacy and sensitivity of the toxicological tools, which, by their inherent nature, allow the overall effects of complex mixtures to be taken into account.

The performance evaluation of wastewater service: a protocol based on performance indicators applied to sewer systems and wastewater treatment plants.

This research aimed to identify a tool to objectively analyse the performance and the environmental contextualisation of sewer systems (SwSs) and wastewater treatment plants (WWTPs). This procedure performs assessment by calculating performance indices which could be subsequently applied to SwSs and WWTPs with different characteristics. The proposed tool can be applied conveniently over the years by managers of integrated urban water management systems for the analysis of different realities also allowing the evaluation of the effects of upgrades carried out during the management phases. The proposed analysis allows the optimisation of SwSs and can profitably guide the choice and the priority among possible interventions for the sewerage infrastructure and WWTPs providing a verification and evaluation protocol as well as a financial planning tool.

Implementation of circular economy in the management of municipal solid waste in an Italian medium-sized city: A 30-years lasting history.

The Circular Economy model is gaining attention as a key factor for boosting sustainable development. Reducing the consumption of raw materials, as well as increasing the amount of recycled waste, are the current challenges the municipal solid waste management system is called for. In this study, the evolution of the municipal waste management strategies in the city of Brescia was analysed, covering a period of 30 years. The results obtained by a) progressively extending the separate collection with street containers, b) building a Waste to Energy plant, and c) moving to a door to door collection system, were assessed via numerical indicators and mass balances. In order to highlight the complexity of the system, the waste flow, from collection to the achievement of the "end of waste" attribute, was followed. Separate collection with street containers came to a saturation percentage around 40%. The realization of the incineration plant eliminated the direct disposal of waste to landfills. With the introduction of the new collection system, the separately collected waste increased up to over 73%, the per capita amount of collected waste decreased from 685.3 kg/(in y) to 579.6 kg/(in y), and a significant reduction of recyclable materials in the unsorted waste was gained. In the paper, these achievements and their affecting factors are analysed. Moreover, criticalities in the calculation of material recovery indices due to the complexity of the system (72 transformation sites were identified) are discussed.