Hybrid Concepts for MAR with Reclaimed Water for for Nonpotable Reuse (D1.1)
Wastewater reuse is increasingly considered as possible alternative water source for diverse non-potable uses. Among the major questions, defining which water quality for which reuse is required is crucial. If the demand for reclaimed water is seasonal, the question of reclaimed water storage is also essential. Aquifer recharge for further nonpotable reuse can be a solution to address many final reuse applications, including indirect agricultural or landscape irrigation, saltwater intrusion barriers, subsidence mitigation/aquifer replenishment or other non-potable reuses. Most of the aquifer recharge applications of wastewater reuse so far rely on high-pressure membrane systems or even double-membrane combined with advanced oxidation processes. However, when non-potable reuse is targeted, or the replenishment of a threatened aquifer is planned, recharge with high-quality non-potable water could be envisaged as acknowledged by the legislation of several countries. In this report, the performance of hybrid disinfection/filtration and recharge schemes is assessed in comparison to a high-pressure membrane system working under similar conditions. Among the portfolio of available disinfection and filtration technologies, five treatment trains were chosen – combinations of ozone or UV treatment with sand filters or UF membrane and final infiltration or injection – and compared to a double-membrane system (UF+NF). A synthetic secondary effluent (SE) was considered for this conceptual study on the basis of a worldwide survey of typical SE water qualities. The major legislations from the WHO, the USEPA and Australian guidelines were considered to define the water quality to be reached by these hybrid treatment schemes. The low targeted value in suspended solids (10 mg/L) and microbiological contaminants (1 fecal coliform / 100 mL) requires extensive disinfection and filtration processes. The proposed schemes were selected on the base of a large review of typical pollutant removal efficiencies found in the literature. To perform a comparative Life-Cycle Assessment of the different treatment trains, similar assumptions were made in all cases for a hypothetical case study of a 50,000-PE reuse plant downstream of a secondary sewage treatment plant. All five proposed hybrid treatment trains are capable of supplying very high non-potable water quality, and the combination of disinfection, filtration and aquifer passage proved to be an efficient combination for removing suspended solids, residual BOD and microbiological contaminants. The environmental performance of the treatment trains was compared in terms of carbon footprint, but also energy demand, human toxicity, acidification impact and land footprint. Both the energy demand and carbon footprint of hybrid schemes was found to be considerably lower than for a double-membrane system, besides offering an additional storage solution in the aquifer. Thus, there is a significant margin for lowering the environmental impact, energy demand and operational costs if non-potable water quality is sufficient for the reuse goal. However, the legal context and social acceptability may represent barriers for this intended recharge of nonpotable water to the aquifer. This conceptual study has shown the potential of hybrid solutions to provide high-quality non potable water for aquifer recharge and further reuse. A large portfolio of solutions was proposed to reach the intended non-potable uses. To assist the selection of adequate treatment trains, the strengths and weaknesses of the solutions can be summarized in a decision tree taking into account the reuse goal, aquifer type and space availability, and selecting the least energy-intensive solution for a given legal and sociocultural context.