Energy use and carbon footprints differ dramatically for diverse wastewater-derived carbonaceous substrates: An integrated exploration of biokinetics and life-cycle assessment

Abstract

Energy neutrality and reduction of carbon emissions are significant challenges to the enhanced sustainability of wastewater treatment plants (WWTPs). Harvesting energy from wastewater carbonaceous substrates can offset energy demands and enable net power generation; yet, there is limited research about how carbonaceous substrates influence energy and carbon implications of WWTPs with integrated energy recovery at systems-level. Consequently, this research uses biokinetics modelling and life cycle assessment philology to explore this notion, by tracing and assessing the quantitative flows of energy embodied or captured, and by exploring the carbon footprint throughout an energy-intensive activated sludge process with integrated energy recovery facilities. The results indicate that energy use and carbon footprint per cubic meter of wastewater treated, varies markedly with the carbon substrate. Compared with systems driven with proteins, carbohydrates or other short-chain fatty acids, systems fed with acetic acid realized energy neutrality with maximal net gain of power from methane combustion (0.198 kWh) and incineration of residual biosolids (0.153 kWh); and also achieved a negative carbon footprint (72.6 g CO2). The findings from this work help us to better understand and develop new technical schemes for improving the energy efficiency of WWTPs by repurposing the stream of carbon substrates across systems.

Life cycle assessment of nutrient recovery strategies from domestic wastewaters to quantify environmental performance and identification of trade-offs

“…Hence, the way forward in this research is to explore nature-based and hybrid treatment systems wastewater treatment systems 61 . This includes integration of energy recovery through biological pathways, and utilisation of green chemicals that could improve yields and decrease energy consumption 62 , 63 . Furthermore, nature-based solutions combined with scaled decentralization may be better suited for developing countries such as Philippines than chemical-based resource recovery 64 .…”

Carbon source recovery from waste sludge reduces greenhouse gas emissions in a pilot-scale industrial wastewater treatment plant

“…This is primarily due to the difference in the influent quality of industrial and municipal wastewater. Previous studies have reported that the GHG emission intensity of municipal WWTPs varies with wastewater influent quality in the range of 0.1–2.4 kg CO 2 -eq m −3 [ 49 , 50 ]. For municipal WWTPs, the ratio of biodegradable COD to TN is a significant parameter that affects the GHG emissions in the wastewater biological treatment process as direct GHG emissions have been shown to increase from 0.49 to 0.63 CO 2 -eq m −3 with a decreasing COD/TN ratio [ 51 ].…”

Generation of oxidative radicals by advanced oxidation processes (AOPs) in wastewater treatment: a mechanistic, environmental and economic review

“…In particular, they indicated that under regular operation, a conventional wastewater treatment facility is estimated to consume 631.24 kWh of electricity from the grid per year and per 1 PE (person-equivalent), with a corresponding carbon footprint of 1.16240 kg CO 2 -eq/PE (Zawartka et al, 2020). When expressed under the functional unit of one cubic meter of treated wastewater, reported carbon footprint values may range from 0.1 to 2.4 kg CO 2 -eq (Li et al, 2017b;Maktabifard et al, 2020;Wang et al, 2016a). Similarly, a recent study by Maktabifard et al (2020) investigated the carbon footprint of six full-scale wastewater treatment plants, and for those plants fully dependent on the power grid, indirect emissions due to energy consumption accounted for approximately 69-72% of the entire carbon footprint (Maktabifard et al, 2020).…”