Experimental power of laboratory-scale results and transferability to full-scale anaerobic digestion.

Anaerobic digestion is today internationally acknowledged as an environmentally sound process for energy and nutrient recovery from organic wastes, and it is the dominant sludge treatment technology in most countries' wastewater treatment plants. Laboratory- or pilot-scale experiments are commonly used as a first step to investigate the potential of new ideas or to confirm research hypothesis before confirmation in full-scale. The objectives of this study were to investigate transferability of methane yield assessments between laboratory- and full-scale, and to compare the influence of experimental uncertainties on experimental power in parallel continuous digester experiments for the two scales. Both batch experiment data (used in a simple equation), as well as continuous laboratory experiments, could be used to predict full-scale methane yield with a high accuracy (<5% difference). Full-scale digesters significantly outperformed hand-fed laboratory digesters in terms of experimental power regarding relative differences in methane yield between two digesters operated in parallel. However, to justify costly long-term continuous laboratory-scale experiments with sufficient experimental power and potentially high transferability, resources also have to be allocated to measures that ensure a high data quality from full-scale reference facilities.

Environmental performance of wastewater reuse systems: impact of system boundaries and external conditions.

Wastewater reclamation will be a significant part of future water management and the environmental assessment of various treatment systems to reuse wastewater has become an important research field. The secondary treatment process and sludge handling on-site are, especially, electricity demanding processes due to aeration, pumping, mixing, dewatering, etc. used for operation and are being identified as the main contributor for many environmental impacts. This study discusses how the environmental performance of reuse treatment systems may be influenced by surrounding conditions. This article illustrates and discusses the importance of factors commonly treated as externalities and as such not being included in optimization strategies of reuse systems, but that are necessary to environmentally assess wastewater reclamation systems. This is illustrated by two up-stream and downstream processes; electricity supply and the use of sludge as fertilizer commonly practiced in regions considered for wastewater reclamation. The study shows that external conditions can have a larger impact on the overall environmental performance of reuse treatment systems than internal optimizations could compensate for. These results imply that a more holistic environmental assessment of reuse schemes could provide less environmental impacts as externalities could be included in measures to reduce the overall impacts.

Removal of pharmaceutical residues using ozonation as intermediate process step at Linköping WWTP, Sweden.

Pilot tests as basis for the design, implementation and operation of a future full-scale oxidation plant completing the existing sewage treatment in Linköping, Sweden, were performed. Using an ozonation step between bio-sedimentation and post-denitrification processes, the primary goal was the removal of the highest priority substances to effluent water levels that will not cause adverse effects in the recipient considering the natural dilution. The study included initial emission screenings, dose control trials, treatment performance studies and eco-toxicity studies. At an ozone dose of 5 mg O3/L, most substances could be removed. Ecotoxicological tests showed no negative effect for the tested ozone doses. High levels of oxygen into the denitrification could be rapidly reduced in the biology. The number of bacteria in the treated water could be significantly reduced even at relatively low ozone doses. Based on these results, the planning for the full-scale implementation of the treatment system was initiated in 2015.

Efficiency of an emissions payment system for nitrogen in sewage treatment plants - a case study.

An emissions payment system for nitrogen in Swedish sewage treatment plants (STPs) was evaluated using a semi-empirical approach. The system was based on a tariff levied on each unit of nitrogen emitted by STPs, and profitable measures to reduce nitrogen emissions were identified for twenty municipal STPs. This was done through direct involvement with the plant personnel and the results were scaled up to cover all treatment plants larger than 2000 person equivalents in the Swedish tributary areas of the Kattegat and the Baltic Proper. The sum of costs and nitrogen reductions were compared with an assumed command-and-control regulation requiring all STPs to obtain 80% total nitrogen reduction in their effluents. Costs for the latter case were estimated using a database containing standard estimates for reduction costs by six specified measures. For both cases a total reduction target of 3000 tonnes of nitrogen was set. We did not find that the emissions payment system was more efficient in terms of total reduction costs, although some practical and administrative advantages could be identified. Our results emphasize the need to evaluate the performance of policy instruments on a case-by-case basis since the theoretical efficiency is not always reflected in practice.

Municipal wastewater reclamation for non-potable reuse--environmental assessments based on pilot-plant studies and system modelling.

Wastewater reclamation is an upcoming approach that will significantly affect wastewater treatment systems. Despite the fact that technology for treating wastewater to an effluent water quality that meets various quality standards for reuse is already available and applied, the reuse of water is not just a simple and straightforward road. Significant additional energy and civil infrastructure is required to treat the water to a standard that allows it to be safely reused. The total impact of treating and reusing water may be higher than the environmental benefits. Thus, it is crucial the life-cycle impacts from upstream and downstream processes of various reuse technologies, i.e. production of chemicals, energy use, eutrophication, sludge handling, etc. The present paper provides a comprehensive evaluation considering different reuse purposes, treatment technologies and plant size. The results of this study suggest that all these factors are highly significant for the environmental impact of wastewater treatment systems for non-potable applications.

Activated carbon for the removal of pharmaceutical residues from treated wastewater.

Pharmaceutical residues, which pass naturally through the human body into sewage, are in many cases virtually unaffected by conventional wastewater treatment. Accumulated in the environment, however, they can significantly impact aquatic life. The present study indicates that many pharmaceutical residues found in wastewater can be removed with activated carbon in a cost-efficient system that delivers higher resource utilisation and security than other carbon systems. The experiment revealed a substantial separation of the analysed compounds, notwithstanding their relatively high solubility in water and dissimilar chemical structures. This implies that beds of activated carbon may be a competitive alternative to treatment with ozone. The effluent water used for the tests, performed over 20 months, originated from Stockholm's largest sewage treatment plant. Passing through a number of different filters with activated carbon removed 90-98% of the pharmaceutical residues from the water. This paper describes pilot-scale tests performed by IVL and the implications for an actual treatment plant that has to treat up to several thousand litres of wastewater per second. In addition, the advantages, disadvantages and costs of the method are discussed. This includes, for example, the clogging of carbon filters and the associated hydraulic capacity limits of the activated carbon.

Transport and fate of silver as polymer-stabilised nanoparticles and ions in a pilot wastewater treatment plant, followed by sludge digestion and disposal of sludge/soil mixtures: A case study.

A case study of transport and changes in properties of polymer-stabilised Ag NPs is presented in this paper investigating their interaction in different treatment steps within a fully realistic pilot wastewater treatment plant (WWTP), in anaerobic digested sludge, and in soil/sludge mixtures. The fate of the same Ag NPs was tracked in these environments, hence taking the history of the Ag NPs into account. The results show that most of the Ag NPs end up in the sludge (80-100%), also after anaerobically digestion. Furthermore, the fraction of silver in the supernatant was very low after 48 h incubation with silver-containing digested sludge mixed with different soil types. However, when Ag NPs were added directly to the sludge/soil mixture, soluble silver was present in the supernatant with sandy soil, but not with clayey soil. In all, generated findings show that risk assessments and toxicological studies of Ag NPs suspensions must take into account possible chemical and particle transformations upon environmental entry, as silver in general become less soluble when transported to WWTPs and interacting with sludge, and soil.

Chemical-Saving Potential for Membrane Bioreactor (MBR) Processes Based on Long-Term Pilot Trials.

Membrane bioreactors (MBRs) have gained attraction in municipal wastewater treatment because of their capacity to meet strict water quality standards and support water reuse. Despite this, their operational sustainability is often compromised by high resource consumption, especially regarding the use of chemicals for membrane cleaning. This study explores innovative membrane-cleaning strategies to enhance the sustainability of MBR processes. Through long-term pilot trials at Stockholm's largest wastewater treatment plant, this study showed that alternative cleaning strategies can reduce chemical use by up to 75% without sacrificing treatment performance. The results further suggest that these alternative strategies could result in cost reductions of up to 70% and a reduction in environmental impacts by as much as 95% for certain indicators. Given that MBRs play a crucial role in addressing increasing treatment demands and advancing circular water management, the outcomes of this study are beneficial for the broader adoption of MBR processes. These results also have implications for existing installations, offering a pathway to more sustainable wastewater treatment. Moreover, the presented cleaning strategies provide significant opportunities for lowering operational costs and reducing the environmental footprint of new and existing MBR installations.

Bioconversion of food waste to volatile fatty acids: Impact of microbial community, pH and retention time.

Bio-based production of materials from waste streams is a pivotal aspect in a circular economy. This study aimed to investigate the influence of inoculum (three different sludge taken from anaerobic digestors), pH (5 & 10) and retention time on production of total volatile fatty acids (VFAs), VFA composition as well as the microbial community during anaerobic digestion of food waste. The highest VFA production was ∼22000 ± 1036 mg COD/L and 12927 ± 1029 mg COD/L on day 15 using the inoculum acclimated to food waste at pH 10 and pH 5, respectively. Acetic acid was the dominant VFA in the batch reactors with initial alkaline conditions, whereas both propionic and acetic acids were the dominant products in the acidic condition. Firmicutes, Chloroflexi and Bacteroidetes had the highest relative abundance in the reactors. VFA generation was positively correlated to the relative abundance of Firmicutes.

Functionalized magnetic particles for water treatment.

In this study, we have taken the concept of water treatment by functionalized magnetic particles one step forward by integrating the technology into a complete proof of concept, which included the preparation of surface modified beads, their use as highly selective absorbents for heavy metals ions (Zinc, Nickel), and their performance in terms of magnetic separation. The separation characteristics were studied both through experiments and by simulations. The data gathered from these experimental works enabled the elaboration of various scenarios for Life Cycle Analysis (LCA). The LCA showed that the environmental impact of the system is highly dependent on the recovery rate of the magnetic particles. The absolute impact on climate change varied significantly among the scenarios studied and the recovery rates. The results support the hypothesis that chelation specificity, magnetic separation and bead recovery should be optimized to specific targets and applications.

Uncertainty-accounting environmental policy and management of water systems.

Environmental policies for water quality and ecosystem management do not commonly require explicit stochastic accounts of uncertainty and risk associated with the quantification and prediction of waterborne pollutant loads and abatement effects. In this study, we formulate and investigate a possible environmental policy that does require an explicit stochastic uncertainty account. We compare both the environmental and economic resource allocation performance of such an uncertainty-accounting environmental policy with that of deterministic, risk-prone and risk-averse environmental policies under a range of different hypothetical, yet still possible, scenarios. The comparison indicates that a stochastic uncertainty-accounting policy may perform better than deterministic policies over a range of different scenarios. Even in the absence of reliable site-specific data, reported literature values appear to be useful for such a stochastic account of uncertainty.

The influence of metal source uncertainty on cost-effective allocation of mine water pollution abatement in catchments.

In mine water pollution abatement, it is commonly assumed that known mine waste sites are the major pollution sources, thus neglecting the possibility of significant contribution from other old and diffuse sources within a catchment. We investigate the influence of different types of pollution source uncertainty on cost-effective allocation of abatement measures for mine water pollution. A catchment-scale cost-minimization model is developed and applied to the catchment of the river Dalälven, Sweden, in order to exemplify important effects of such source uncertainty. Results indicate that, if the pollution distribution between point and diffuse sources is partly unknown, downstream abatement measures, such as constructed wetlands, at given compliance boundaries are often cost-effective. If downstream abatement measures are not practically feasible, the pollution source distribution between point and diffuse mine water sources is critical for cost-effective solutions to abatement measure allocation in catchments. In contrast, cost-effective solutions are relatively insensitive to uncertainty in total pollutant discharge from mine water sources.

Novel quantification of coupled natural and cross-sectoral water and nutrient/pollutant flows for environmental management.

Human water use and anthropogenic water pollution and ecosystem deterioration have increased so much that it is now a strategic challenge to maximize benefits from various possible water uses, while ensuring that basic human needs are met and the environment is protected. We propose and develop a novel use of input-output flow analysis as a relatively simple, compact and powerful tool for quantification of coupled natural and cross-sectoral flows of water, nutrients, and pollutants in catchments. The tool quantifies implications of various environmental regulation and management scenarios for both natural water systems and engineered-economic systems and sectors that use and impact natural waters for meeting human needs. Specific case study application to water and nitrogen flows in the Swedish Norrström drainage basin indicates considerable nitrogen load contributions to surface and coastal waters from slow groundwater flow paths and legacies of accumulated nitrogen in subsurface and immobile water pools. This implies that effective nitrogen load abatement cannot focus only on active sources but must also include downstream measures, which can capture and abate nitrogen/pollutant loading from different types of known and yet unknown point and diffuse sources within associated catchments.