Abstract
To understand characteristics of on-line oxidation-reduction potential (ORP) in a subsurface wastewater infiltration system (SWIS) under different intermittent influent conditions, ORP among five matrix depths at wet-dry ratios (Rwds) of 2:1, 1:1 and 1:2 with a hydraulic load of 0.10 m3·(m2·d)−1 were monitored. Results showed that the optimal Rwd for the SWIS was 1:1. In that case, ORP at 40 and 65 cm depths changed significantly, by 529 mV and 261 mV, respectively, from the inflow period to the dry period, which was conducive to the recovery of the oxidation environment. It was concluded that ORP varied nonlinearly in strongly aerobic and hypoxic environment. Wastewater was fed into the SWIS at 80 cm and dissolved oxygen diffused at the initial period of one cycle. As a consequence, ORP at 65 cm increased with water content increasing. However, ORP at 40 and 95 cm displayed inverse trends. Moreover, results showed that ORP decreased with Fe2+ and Mn2+ increasing under aerobic conditions (p < 0.05) because Fe2+ and Mn2+ moved with wastewater flow. Effluent met reuse requirements and no clogging was found in the SWIS during the operation.
Highlights
Facing with multiple challenges of energy shortage, resource depletion and environmental pollution, sustainability is considered to be a pivotal criterion and driving force to further advancement [1]
The study demonstrated that oxidation-reduction potential (ORP) changes were non-linear with Rwd s changing
ORP at 40 and 95 cm depths decreased during inflow periods and increased rapidly during dry periods
Summary
Facing with multiple challenges of energy shortage, resource depletion and environmental pollution, sustainability is considered to be a pivotal criterion and driving force to further advancement [1]. There are many green technologies to achieve sustainable wastewater treatment, such as microbial fuel cells-centered technologies and membrane technologies, which can be applied in textile and saline water [2]. Compared with membrane technologies, which generate membrane wastewater during the membrane fabrication processes, subsurface wastewater infiltration systems (SWISs), as representatives of decentralized sewage treatment, are considered to be satisfactory biological reactors with low construction and operation expenses, satisfactory pollutant removal performances and lower cost of maintenance [3,4]. In contrast to soil self-purification, sewage is fed into to a certain depth of SWISs and infiltrated to oxic areas evenly by capillary and gravity forces [5]. In the case of this condition, pollutants are removed by a series of physical, chemical and biological reactions
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