Economic construction and operation of hectare-scale wastewater treatment enhanced pond systems

Abstract

Enhanced pond systems (EPS) are an effective and economic upgrade option for conventional wastewater treatment ponds providing improved natural disinfection and nutrient removal. Moreover, wastewater nutrients are recovered as harvested algal biomass for beneficial use as fertiliser, feed or biofuel feedstock. Low-cost construction and operation are crucial factors for the adoption of EPS. This paper presents novel and economic design, construction and operation methods for an earthen hectare-scale EPS treating domestic wastewater at the Cambridge Wastewater Treatment Plant, New Zealand. The system consisted of: the existing Anaerobic Pond to settle and anaerobically digest wastewater solids that was retrofitted with a cover to capture the biogas, two 1-hectare HRAPs to aerobically treat and remove nutrients from the anaerobic pond effluent through the production of algal biomass, algal harvest ponds to settle and concentrate the algal biomass which was then pumped into a covered digester pond to recover energy as biogas and nutrients as a concentrated digestate. Further effluent polishing was provided by maturation ponds and rock filters to achieve higher quality effluent. All of the ponds were of earthen construction and were made within existing or disused conventional wastewater treatment ponds. Cost-effective earthen pond construction combined with the use of protective geotextile and geomembrane liners, geomembrane covers, painted steel paddlewheels and precast concrete carbonation sumps enable economic implementation of EPS for energy-efficient and effective wastewater treatment as well as nutrient recovery and energy production for the local community.