• Energy Research

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.

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.

A study of bacterial populations in metropolitan Adelaide domestic reticulation pipes was conducted to investigate a possible link between copper in drinking water and biofilms. Biofilm densities from cold water copper pipes at 10 sample sites were measured by viable cell counts. The range detected was from < 2 x 10(1) to 3.25 x 10(7) cfu cm-2. Five isolates were selected for further experiments as they represented a range of responses to solvated copper and relative tendency for adhesion on glass slides. Drinking water supplied to the Adelaide Hills is high in total organic carbon (TOC; 22.57 mg Cl-1) and has a negative Langelier Index (LI;-1.16), whereas Adelaide metropolitan water undergoes filtration and has both a lower TOC and LI (10.72 mg Cl-1, LI,-0.49). Copper coupons were exposed to biofilm isolates (24h), washed and resuspended in Adelaide metropolitan and Adelaide Hills water. Copper coupons not exposed to biofilm isolates were suspended in respective waters as a control. After 5 d of incubation, the copper content of Adelaide Hills water (4.71 +/- 0.87 mg Cu l-1), in which the copper coupons were suspended, consistently exceeded values obtained in the metropolitan Adelaide water (1.17 +/- 0.249 mg Cu l-1). The concentration of copper in the Adelaide Hills water was influenced by the bacterial species forming the biofilm on the coupon, with Agrobacterium sp. producing significantly higher levels of soluble copper than the control. The experiments reported here indicate that the suspended organic carbon, the aggressivity of the water and the biofilm may independently or synergistically increase the dissolution of copper from pipes into drinking water.

A study of bacterial populations in metropolitan Adelaide domestic reticulation pipes was conducted to investigate a possible link between copper in drinking water and biofilms. Biofilm densities from cold water copper pipes at 10 sample sites were measured by viable cell counts. The range detected was from < 2 x 10(1) to 3.25 x 10(7) cfu cm-2. Five isolates were selected for further experiments as they represented a range of responses to solvated copper and relative tendency for adhesion on glass slides. Drinking water supplied to the Adelaide Hills is high in total organic carbon (TOC; 22.57 mg Cl-1) and has a negative Langelier Index (LI;-1.16), whereas Adelaide metropolitan water undergoes filtration and has both a lower TOC and LI (10.72 mg Cl-1, LI,-0.49). Copper coupons were exposed to biofilm isolates (24h), washed and resuspended in Adelaide metropolitan and Adelaide Hills water. Copper coupons not exposed to biofilm isolates were suspended in respective waters as a control. After 5 d of incubation, the copper content of Adelaide Hills water (4.71 +/- 0.87 mg Cu l-1), in which the copper coupons were suspended, consistently exceeded values obtained in the metropolitan Adelaide water (1.17 +/- 0.249 mg Cu l-1). The concentration of copper in the Adelaide Hills water was influenced by the bacterial species forming the biofilm on the coupon, with Agrobacterium sp. producing significantly higher levels of soluble copper than the control. The experiments reported here indicate that the suspended organic carbon, the aggressivity of the water and the biofilm may independently or synergistically increase the dissolution of copper from pipes into drinking water.

Abstract A high rate algal pond (HRAP) incorporated into a community wastewater management scheme was operated over two years in the Mediterranean climate of Kingston on Murray, South Australia. Uniquely, the study evaluated the performance of the HRAP when fed (12 m3 day−1) either treated effluent from on-site septic tanks or a facultative pond further treating the septic tank effluent from within the community (population 300). The influence of depth and season on wastewater treatment and biomass production were determined for both configurations. Generally, wastewater treatment (>90% BOD5 removed) and biomass production (31.7 g m−2 day−1) was improved when the HRAP was fed septic tank effluent. PO4-P removal was low and effected by biomass uptake rather than precipitation. Inorganic nitrogen removal was independent of depth in the warmer months and inversely related to depth in the colder months. The mean log10 removal values for Escherichia coli were 1.75 and 2.75 for the HRAP when fed septic and facultative pond effluent respectively. In the prevailing Mediterranean climate, adequate BOD5 and nitrogen removal, and disinfection assessed using E. coli as the faecal indicator organism was achieved at 0.32 m depth at a retention time of 4 days.

Abstract A high rate algal pond (HRAP) incorporated into a community wastewater management scheme was operated over two years in the Mediterranean climate of Kingston on Murray, South Australia. Uniquely, the study evaluated the performance of the HRAP when fed (12 m3 day−1) either treated effluent from on-site septic tanks or a facultative pond further treating the septic tank effluent from within the community (population 300). The influence of depth and season on wastewater treatment and biomass production were determined for both configurations. Generally, wastewater treatment (>90% BOD5 removed) and biomass production (31.7 g m−2 day−1) was improved when the HRAP was fed septic tank effluent. PO4-P removal was low and effected by biomass uptake rather than precipitation. Inorganic nitrogen removal was independent of depth in the warmer months and inversely related to depth in the colder months. The mean log10 removal values for Escherichia coli were 1.75 and 2.75 for the HRAP when fed septic and facultative pond effluent respectively. In the prevailing Mediterranean climate, adequate BOD5 and nitrogen removal, and disinfection assessed using E. coli as the faecal indicator organism was achieved at 0.32 m depth at a retention time of 4 days.

The interference of ammonia with the chlorination process is a problem for many reclaimed water treatment plant operators. This paper presents the findings from a series of pilot experiments that investigated the efficacy of high flow rate nitrifying trickling filters (NTFs) for the removal of low concentrations of ammonia (0.5–3.0 mg N L−1) from reclaimed wastewater. Results showed that nitrification was impeded by a combination of high organic carbon loads and aquatic snails, which consumed much of the active biomass. With adequate snail control, nitrification rates (0.3–1.1 g NH4-N m−2 d−1) equivalent to that of traditional wastewater NTFs were achieved, despite operating under comparably low ammonia feed concentrations and high hydraulic flow rates.

The interference of ammonia with the chlorination process is a problem for many reclaimed water treatment plant operators. This paper presents the findings from a series of pilot experiments that investigated the efficacy of high flow rate nitrifying trickling filters (NTFs) for the removal of low concentrations of ammonia (0.5–3.0 mg N L−1) from reclaimed wastewater. Results showed that nitrification was impeded by a combination of high organic carbon loads and aquatic snails, which consumed much of the active biomass. With adequate snail control, nitrification rates (0.3–1.1 g NH4-N m−2 d−1) equivalent to that of traditional wastewater NTFs were achieved, despite operating under comparably low ammonia feed concentrations and high hydraulic flow rates.