In-building heat recovery mitigates adverse temperature effects on biological wastewater treatment: A network-scale analysis of thermal-hydraulics in sewers.

Heat recovery from wastewater is a robust and straightforward strategy to reduce water-related energy consumption. Its implementation, though, requires a careful assessment of its impacts across the entire wastewater system as adverse effects on the water and resource recovery facility and competition among heat recovery strategies may arise. A model-based assessment of heat recovery from wastewater therefore implies extending the modeling spatial scope, with the aim of enabling thermal-hydraulic simulations from the household tap along its entire flow path down to the wastewater resource recovery facility. With this aim in mind, we propose a new modeling framework interfacing thermal-hydraulic simulations of (i) households, (ii) private lateral connections, and (iii) the main public sewer network. Applying this framework to analyze the fate of wastewater heat budgets in a Swiss catchment, we find that heat losses in lateral connections are large and cannot be overlooked in any thermal-hydraulic analysis, due to the high-temperature, low-flow wastewater characteristics maximizing heat losses to the environment. Further, we find that implementing shower drain heat recovery devices in 50% of the catchment's households lower the wastewater temperature at the recovery facility significantly less - only 0.3 K - than centralized in-sewer heat recovery, due to a significant thermal damping effect induced by lateral connections and secondary sewer lines. In-building technologies are thus less likely to adversely affect biological wastewater treatment processes. The proposed open-source modeling framework can be applied to any other catchment. We thereby hope to enable more efficient heat recovery strategies, maximizing energy harvesting while minimising impacts on biological wastewater treatment.

Not all SuDS are created equal: Impact of different approaches on combined sewer overflows.

Sustainable urban drainage systems (SuDS) help in stormwater management by reducing runoff volume, increasing runoff concentration time and thereby improving the drainage system capacity. This study investigated the potential and cost-effectiveness of SuDS in reducing combined sewer overflows (CSOs). We simulated the performance of four SuDS techniques (bioretention cell, permeable pavement, rain barrel and green roof) at incremental levels of spatial coverage for a small urban catchment with a combined sewer system. We also used an Analytic Hierarchy Process (AHP) considering end-point CSO, land use, imperviousness, slope and elevation criteria to identify priority areas for SuDS deployment. Results showed that CSO volume attenuation ranged a maximum of 50-99% for the catchment, depending on the deployment strategy and underlying mechanisms of each technology. We also found that deployment of SuDS in AHP-selected sub-catchments improved CSO reduction only for rain barrels and green roofs, but not for bioretention cells and permeable pavements. SuDS were also a cost-effective retrofit option: for a 40% volume reduction, the SuDS cost, at most, 25% of the equivalent cost required for a large CSO tank. Outcomes of this study demonstrate the efficacy of SuDS in controlling CSOs, adding yet another tangible benefit to their increasingly recognised multi-functionality.

Sustainable management practices of food waste in Asia: Technological and policy drivers.

The policies and technological drivers to manage food waste in Asia have been shaped by the increasing awareness of the countries to this issue, their commitment to national and international development goals, their socio-economic constraints, and their recognition of the potency to recover nutrients and energy from food waste. The concept of reduce, reuse and recycle (the 3R principles) streamline the existing food waste management policies, and scrutinising the gaps and challenges led to a conclusion that most of the countries emphasise food waste segregation and treatment instead of prevention at source itself. Furthermore, a qualitative SWOT analysis of five prevailing treatment options led to a conclusion that animal feeding, incineration, and landfilling are unsustainable since they pose various health and environmental hazard risks. It was further concluded that anaerobic digestion was the preferred option than aerobic digestion (composting) considering the characteristics of the available food waste in Asia as well as the underlying environmental and economic benefits. Moreover, decentralised, community-scale, anaerobic digestion system has been gaining traction over centralised, large-scale system because of their lower energy footprint, ease of operation, need for lesser resources, lower operation and maintenance costs, and higher chances of public acceptance. It was also observed that the policy to gain energy from segregated food waste is a larger driving force for the efforts to promote anaerobic digestion and thereby manage food waste sustainably.