Estimation of Energy Recovery Potential from Primary Residues of Four Municipal Wastewater Treatment Plants

Abstract

Wastewater treatment plants have been traditionally developed for the aerobic degradation of effluent organic matter, and are associated with high energy consumption. The adoption of sustainable development targets favors the utilization of every available energy source, and the current work aims at the identification of biomethane potential from non-conventional sources derived from municipal wastewater treatment processes. Byproducts derived from the primary treatment process stage were collected from four sewage treatment plants in Greece with great variation in design capacity and servicing areas with wide human activities, affecting the quality of the influents and the corresponding primary wastes. The samples were characterized for the determination of their solids and fats content, as well as the concentration of leached organic matter and nutrients, and were subjected to anaerobic digestion treatment for the measurement of their biomethane production potential according to standardized procedures. All samples exhibited potential for biogas utilization, with screenings collected from a treatment plant receiving wastewater from an area with combined rural and agro-industrial activities presenting the highest potential. Nevertheless, these samples had a methanogens doubling time of around 1.3 days, while screenings from a high-capacity unit proved to have a methanogens doubling time of less than 1 day. On the other hand, floatings from grit chambers presented the smallest potential for energy utilization. Nevertheless, these wastes can be utilized for energy production, potentially in secondary sludge co-digestion units, converting a treatment plant from an energy demanding to a zero energy or even a power production process.

Energy Valorization of Fine Screenings from a Municipal Wastewater Treatment Plant

“…The biochemical methane potential (BMP) was measured using the anaerobic digestion treatment described in [9]. Briefly, certain amounts of samples and inoculum were placed in 300 mL glass reactors following incubation at 37 • C. A sample from the contents of the sludge anaerobic digester of the full-scale municipal wastewater treatment plant was used as the inoculum.…”

“…The biochemical methane production potential was measured in an energy utilization study of the primary screenings and floatings from four municipal wastewater treatment plants, and it was found to range from values as low as 90 L/kg VS up to 740 L/kg VS for fine screenings, which is considerably higher than the normal biochemical methane potential of excess sludge, which varies between 300 and 400 L/kg VS [9]. In the same study, it was observed that floatings had a rather low methane production potential, despite their high fat content, due to the presence of cellulosic fibers with a low degradation potential and the occurrence of long-chain fatty acids inhibiting the anaerobic process.…”

Promoting Sustainability: Wastewater Treatment Plants as a Source of Biomethane in Regions Far from a High-Pressure Grid. A Real Portuguese Case Study

“…The indicators usually used to conclude if a project is profitable (enough) or not are the net present value (NPV), discounted payback time (DPBT), internal rate of return (IRR) and profitability index (PI). These indicators are calculated by means of Equation (1) to Equation (4). NPV establishes the difference between the present value of cash inflows and cash outflows over a period of time.…”

“…The need to find a replacement for fossil fuels emerged both because of the scarcity of known non-renewable fuel reserves and because of the environmental problems caused by greenhouse gas (GHG) emissions [2,3]. In this context, renewable energies have become important in the last decades mainly because of the sources from where they come [4,5]. Indeed, the global total primary renewable energy supply in the world reached around 80 EJ in 2018, with an average annual growth rate of 2.0% since 1990 [6].…”

Investigations into valorisation of trade wastewater for biomethane production

“…Some studies have mapped potential areas for large scale co-digestion power plants using high level theoretical data based on industry type [ 10 ], while others have devised systems of classification for wastewater to visualise recycling and industrial symbiosis opportunities [ 25 , 26 ] However, the practical screening of raw and pre-treated wastewaters to determine the suitability of individual small-scale biogas fermentation has, to the authors’ best knowledge, not been reported in the literature. Recent studies have investigated and compared digestion of treatment plant sludges [ 27 ], but not substrates from a step earlier in wastewater treatment, i.e. at the site of wastewater generation.…”