Mini-review: high rate algal ponds, flexible systems for sustainable wastewater treatment

Abstract

Over the last 20 years, there has been a growing requirement by governments around the world for organisations to adopt more sustainable practices. Wastewater treatment is no exception, with many currently used systems requiring large capital investment, land area and power consumption. High rate algal ponds offer a sustainable, efficient and lower cost option to the systems currently in use. They are shallow, mixed lagoon based systems, which aim to maximise wastewater treatment by creating optimal conditions for algal growth and oxygen production-the key processes which remove nitrogen and organic waste in HRAP systems. This design means they can treat wastewater to an acceptable quality within a fifth of time of other lagoon systems while using 50% less surface area. This smaller land requirement decreases both the construction costs and evaporative water losses, making larger volumes of treated water available for beneficial reuse. They are ideal for rural, peri-urban and remote communities as they require minimum power and little on-site management. This review will address the history of and current trends in high rate algal pond development and application; a comparison of their performance with other systems when treating various wastewaters; and discuss their potential for production of added-value products. Finally, the review will consider areas requiring further research.

Independent validation and regulatory agency approval for high rate algal ponds to treat wastewater from rural communities

“…The observed variation in the daily flows was due to the fluctuations in the population of the township and was not subject to a regular, predictable pattern. The mean daily flow was 12 m 3 , consistent with the long-term average. The daily inflow comes from a central pumping station in the township, which is activated and deactivated by float switches.…”

“…The mean BOD 5 removal from the inlet wastewater following treatment in HRAP1 was consistent with that reported for longitudinal studies on the same pond, 91.76% and 93.4%, 1,23 and similar to removal rates reported for other HRAPs treating domestic wastewater. 3 Following treatment in HRAP2, the mean BOD 5 concentration at the outlet of HRAP2 was 23.85 ± 10.92 mg BOD 5 L −1 , higher than the HRAP2 inlet water supplied from HRAP1 and independent-samples Mann-Whitney U test showed that this difference was statistically significant (p = 0.007; n = 40). The most likely reason for the increased BOD 5 concentration in HRAP2 is that the ageing biomass in the pond was degrading and releasing extracellular material into suspension, increasing the organic matter concentration.…”

“…1,2 This reduction in treatment time reduces area requirement and consequently construction costs, while the reduced evaporative loss means more water is available for beneficial reuse in water-scare regions, such as, rural Australia. 3 After establishing the many benefits HRAPs provide over WSPs, approval for HRAPs to be included as an alternative treatment option to WSPs in the CWMS design guidelines was sought from the South Australian Department of Health, Wastewater Management Group (DoHWMG). The validation process required for approval is consistent with the Australian National Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 1), 4 which employ the concept of disability-adjusted life years (DALYs) with the tolerable risk accepted as 10 −6 DALYs per capita per year, equivalent to an annual risk of diarrhoeal illness of 1 per 1000 people.…”

Microalgae wastewater treatment: Biological and technological approaches

“…Pond systems are common in bacterial WWT . They are also the most widely applied type of large‐scale reactor for microalgae cultivation, because of their simple construction and low investment costs .…”

Investigation and modelling of high rate algal ponds utilising secondary effluent at Western Water, Bacchus Marsh Recycled Water Plant

“…Solar radiation is the primary form of energy for microalgae, as they are photosynthetic organisms . Most algae have an optimal solar radiation range in which they prefer to grow, and the shallow design of HRAPs maximises the amount of light for algal growth (Young et al 2017). Regular harvesting and mixing can help minimise self-shading that occurs at high concentrations.…”