Unravelling the environmental and economic impacts of innovative technologies for the enhancement of biogas production and sludge management in wastewater systems

Increasing resource circularity in wastewater treatment: Environmental implications of technological upgrades

A paradigm shift is needed in wastewater treatment plants (WWTPs) to progress from traditional pollutant removal to resource recovery. However, whether this transformation produces overall environmental benefits will depend on the efficient and sustainable use of resources by emerging technologies. Given that many of these technologies are still being tested at the pilot scale, there is a lack of environmental assessments quantifying their impacts and benefits. In particular, an integrated approach to energy and nutrient recovery can elucidate the potential configurations for WWTPs. In this study, we conduct a life cycle assessment (LCA) of emergent wastewater treatment technologies aimed at increasing resource circularity in WWTPs. We focus on increasing energy self-sufficiency through biogas upgrades and a more radical circular approach aimed at nutrient recovery. Based on a case-study WWTP, we compare its current configuration with (1) implementing autotrophic nitrogen removal in the mainstream and deriving most of the organic matter for biogas production, which increases the quality and quantity of biogas available for energy production; (2) implementing struvite recovery through enhanced biological phosphorus removal (EBPR) as a radical approach to phosphorus management, offering an alternative to mineral fertilizer; and (3) a combination of both approaches. The results show that incremental changes in biogas production are insufficient for compensating for the environmental investment in infrastructure, although autotrophic nitrogen removal is beneficial for increasing the quality of the effluent. Combined phosphorus and energy recovery reduce the environmental impacts from the avoided use of fertilizers and phosphorus and the nitrogen release into water bodies. An integrated approach to resource management in WWTPs is thus desirable and creates new opportunities toward the implementation of circular strategies with low environmental impact in cities.

Evaluating Fertilizer-Drawn Forward Osmosis Performance in Treating Anaerobic Palm Oil Mill Effluent

Fertilizer-drawn forward osmosis (FDFO) is a potential alternative to recover and reuse water and nutrients from agricultural wastewater, such as palm oil mill effluent that consists of 95% water and is rich in nutrients. This study investigated the potential of commercial fertilizers as draw solution (DS) in FDFO to treat anaerobic palm oil mill effluent (An-POME). The process parameters affecting FO were studied and optimized, which were then applied to fertilizer selection based on FO performance and fouling propensity. Six commonly used fertilizers were screened and assessed in terms of pure water flux (J_w) and reverse salt flux (J_S). Ammonium sulfate ((NH₄)₂SO₄), mono-ammonium phosphate (MAP), and potassium chloride (KCl) were further evaluated with An-POME. MAP showed the best performance against An-POME, with a high average water flux, low flux decline, the highest performance ratio (PR), and highest water recovery of 5.9% for a 4-h operation. In a 24-h fouling run, the average flux decline and water recovered were 84% and 15%, respectively. Both hydraulic flushing and osmotic backwashing cleaning were able to effectively restore the water flux. The results demonstrated that FDFO using commercial fertilizers has the potential for the treatment of An-POME for water recovery. Nevertheless, further investigation is needed to address challenges such as J_S and the dilution factor of DS for direct use of fertigation.

Evaluation of Synergies of a Biomass Power Plant and a Biogas Station with a Carbon Capture System

The global carbon emissions from the tertiary sector have increased during the last years, becoming a target sector for carbon capture technologies. This study analyzes the potential application of a carbon capture system (CCS) to the usage of biogas from a livestock waste treatment plant (LWTP) and solid biomass. The proposed BECCS system fulfils the requirement of energy demands of the LWTP and generates electricity. The CCS is sized to consume the biogas produced and the selected operation parameters ensure a high capture efficiency. The BECCS is completed by a Rankine cycle fed by solid biomass and waste heat from the capture process is sized and implemented to produce electricity and steam. The proposed concept handles 1534 kW of solid biomass and 1398 kW of biogas to produce 746.20 kWe and cover the heat demand of a LWTP, 597 kWth. The avoided CO2 emissions sum up to 1620 ton CO2/year. The economic calculations show the limitation of this concept deployment under current prices of electricity and CO2 allowances. Results show the potential feasibility under future scenarios with 5 to 6 payback periods whenever public policies support the use of CCS and EU ETS evolves towards higher prices of carbon allowances.

Life Cycle Assessment of Municipal Wastewater Treatment Processes Regarding Energy Production from the Sludge Line

The efficient and timely removal of organic matter and nutrients from water used in normal municipal functions is considered to be the main task of wastewater treatment plants (WWTPs). Therefore, these facilities are considered to be essential units that are required to avoid pollution of the water environment and decrease the possibility of triggering eutrophication. Even though these benefits are undeniable, they remain at odds with the high energy demand of wastewater treatment and sludge processes. As a consequence, WWTPs have various environmental impacts, which can be estimated and categorized using Life Cycle Assessment (LCA) analysis. In this study, a municipal WWTP based in Poznań, Poland, was examined using the method defined in ISO 14040. ReCiPe Endpoint and Midpoint (v1.11), in a hierarchical approach, were used to evaluate the environmental impacts regarding 18 different categories. All calculations were conducted using a detailed database from 2019, which describes each chosen facility. It was found that the energy component, related to the wastewater treatment process demand and electricity production, is the main determinant of the sum of the environmental impact indicators in light of the modelled energy mix. Therefore, it determines the entire process as an environmentally friendly activity.