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Filamentous algae nutrient scrubber (FANS) operating parameters can strongly influence algal biomass productivity and nutrient removal. However, few studies to date have investigated the effects of FANS operating parameters such as initial standing crop, harvesting frequency and influent flow rate on biomass productivity and nutrient removal performance, especially for FANS that cultivate a single species of algae. Therefore, the overall aim of this study was to investigate how operating parameters affect the biomass productivity and nutrient removal performance of Oedogonium sp. - a promising species for unialgal FANS. The initial standing crop had a significant effect on biomass productivity, with productivities being highest (8.6 ± 0.5 g DW biomass m -2 day -1 ) when the initial standing crop was 60-70 g DW m -2 . However, the daily nutrient removal rate was highest (0.47 ± 0.06 g N m -2 day -1 and 1.24 ± 0.13 g P m -2 day -1 ) at the highest initial standing crop (100-110 DW m -2 ). Biomass productivity was highest with a three-day growth period, regardless of size of the initial standing crop. Therefore, a four-day harvesting interval was selected as the optimal harvesting regime to promote exponential growth and high biomass production. Influent flow rate had a significant effect on biomass productivity, which was highest (9.3 ± 1.7 g DW m -2 day -1 ) for the 1 L min -1 flow rate. This flow rate also gave the highest instantaneous nutrient removal rate (0.05 ± 0.02 g N m -3 and 0.14 ± 0.05 g P m -3 ). Current results suggest that an optimum initial standing crop of 70-80 g DW m -2 , harvesting frequency of four days and influent flow rate of 1 L min -1 (16.7 L min -1 m -1 width) were optimal for Oedogonium sp. cultivated on FANS to maximize their biomass production and nutrient removal under controlled laboratory conditions. These results contribute to understanding the impacts of operating parameters on optimizing unialgal Oedogonium sp. FANS biomass production and nutrient removal performance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

We investigated the effect of algal contact time (ACT) and horizontal water velocity (HWV) on the performance of pilot-scale Filamentous Algae Nutrient Scrubbers (FANS) treating river water during the NZ summer. The FANS floways were seeded with a mixture of four New Zealand native filamentous algal species (Oedogonium sp., Cladophora sp., Rhizoclonium sp., and Spirogyra sp.) and allowed to establish over one month. River water was pumped onto the top of each FANS at different flow rates (2, 4 or 8 L min -1 ) to give ACTs from 0.6 to 10.1 min depending on FANS length (6-24 m) and HWV from 0.04 to 0.16 m s -1 . FANS inflow and final outflows were monitored three times a week for nitrate and DRP concentrations and FANS algal biomass was harvested weekly. Average biomass productivity was significantly higher on the FANS with shorter ACT. For example, biomass productivity of the 24 m length FANS with 2.5 min ACT were 67% higher (11.2 g DW m -2 d -1 ) than that with four times the ACT (10.1 min). Irrespective of the HWV the biomass productivity declined down the length of the floways (with longer ACT) and the decline was greater at lower HWV. The decreased biomass productivity at lower HWV (and/or higher ACT) was likely attributable to the daytime carbon limitation of photosynthesis (at pH > 9.5) and heat stress with elevated daytime water temperature (at >30 °C). Despite the short ACT (<10.1 min) the single pass pilot-scale FANS effectively removed both nitrate-N and DRP from the river water, with >35% removal of both NO 3 -N (from 0.49 to <0.32 mg N L -1 ) and DRP (from 0.14 to <0.09 mg P L -1 ). Both the nitrogen and phosphorus content of the harvested algal biomass were unaffected by both HWV and ACT and typical (N: ∼2.0%; P: 0.2-0.3%) of the literature values (N: 1.5-3.0%; P: 0.15-0.32%). Compared with constructed wetland nutrient removal (0.1 g N m -2 d -1 ; 0.08 g P m -2 d -1 ), the FANS achieved up to 2.5-fold higher nitrogen removal (0.24 N m -2 d -1 ) through algal nitrogen assimilation followed by subsequent algal harvest and up to 4-fold higher phosphorus removal (0.34 g P m -2 d -1 ) through a combination of algal phosphorus assimilation and some P-precipitation under photosynthesis-mediated elevated daytime pH levels (pH > 9.0). This research indicates that FANS have the potential to require less than half the land area of constructed wetlands for the same level of nitrogen removal and that they require only a few weeks to establish to achieve full performance. Moreover, FANS have the further benefit of resource recovery for beneficial re-use of harvested algal biomass for animal feed, fertiliser, or biofuel., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study compared light and dark disinfection of faecal bacteria/viral indicator organisms (E. coli and MS2 (fRNA) bacteriophage) and human viruses (Echovirus and Norovirus) in Wastewater Treatment Pond (WTP) mesocosms. Stirred pond mesocosms were operated in either outdoor sunlight-exposed or laboratory dark conditions in two experiments during the austral summer. To investigate wavelength-dependence of sunlight disinfection, three optical filters were used: (1) polyethylene film (light control: transmitting all solar UV and visible wavelengths), (2) acrylic (removing most UVB <315 nm), and (3) polycarbonate (removing both UVB and UVA <400 nm). To assess different dark disinfection processes WTP effluent was treated before spiking with target microbes, by (a) 0.22 μm filtration to remove all but colloidal particles, (b) 0.22 μm filtration followed by heat treatment to destroy enzymes, and (c) addition of Cytochalasin B to supress protozoan grazing. Microbiological stocks containing E. coli, MS2 phage, Echovirus, and Norovirus were spiked into each mesocosm 10 min before the experiments commenced. The light control exposed to all sunlight wavelengths achieved >5-log E. coli and MS2 phage removal (from ~1.0 × 10 6 to <1 PFU/mL) within 3 h compared with up to 6 h in UV-filtered mesocosms. This result confirms that UVB contributes to inactivation of E. coli and viruses by direct sunlight inactivation. However, the very high attenuation with depth of UVB in WTP water (99% removal in the top 8 cm) suggests that UVB disinfection may be less important than other removal processes averaged over time and full-scale pond depth. Dark removal was appreciably slower than sunlight-mediated inactivation. The dark control typically achieved higher removal of E. coli and viruses than the 0.22 μm filtered (dark) mesocosms. This result suggests that adsorption of E. coli and viruses to WTP particles (e.g., algae and bacteria bio-flocs) is an important mechanism of dark disinfection, while bacteria and virus characteristics (e.g. surface charge) and environmental conditions can influence dark disinfection processes., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Enhanced pond systems (EPS) consist of a series of ponds that have been designed to work in synergy to provide both cost-effective enhanced wastewater treatment and resource recovery, in the form of algal biomass, for beneficial reuse. Due to the limited number of full-scale EPS systems worldwide, our understanding of factors governing both enhanced wastewater treatment and resource recovery is limited. This paper investigates the seasonal performance of a full-scale municipal wastewater EPS with respect to nutrient removal from the liquid fraction, microalgal biomass production and subsequent removal through the system. In the high rate algal pond both microalgal productivity (determined as organic matter and chlorophyll a biomass) and NH 4 -N removal varied seasonally, with significantly higher biomass and removal rates in summer than in spring (p < 0.05) or winter (p < 0.01). Microalgal biomass was not successfully harvested in the algal harvester pond (AHP), most likely due to poor flocc formation coupled with relatively short hydraulic residence time (HRT). High percentage removal rates, from sedimentation and zooplankton grazing, were achieved in the maturation pond (MP) series, particularly in winter and spring. However, in summer decreased efficiency of biomass removal and the growth of new microalgal species suggests that summer-time HRT in the MPs could be shortened. Further modifications to the operation of the AHP, seasonal changes in the HRT of the MPs and potential harvesting of zooplankton grazers are all potential strategies for improving resource recovery and producing a higher quality final discharge effluent., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In the last decade, studies have focused on identifying the most suitable microalgal species for coupled high rate algal pond (HRAP) wastewater treatment and resource recovery. However, one of the challenges facing outdoor HRAP systems is maintaining microalgal species dominance. By increasing our understanding of the environmental drivers of microalgal community composition within the HRAP environment, it may be possible to manipulate the system in such a way to favour the growth of desirable species. In this paper, we investigate the microalgal community composition in two full-scale HRAPs over a 23-month period. We compare wastewater treatment performance between dominant species and identify the environmental drivers that trigger change in community composition. A total of 33 microalgal species were identified over the 23-month period but species richness (the number of species present at any given time) was low and was not related to either productivity or nutrient removal efficiency. Species turnover of the dominant microalgae happened rapidly, typically <1 week. Changes in the influent NH 4 -N concentration and zooplankton grazer numbers were significantly associated with species turnover, accounting for 80% of the changes in dominant species throughout the 23-month study period. Both nutrient removal and biomass production did not differ between the two HRAPs when the dominant species was the same or differed in the two ponds. These results suggest that microalgal functional groups are more important than individual species for full-scale HRAP performance. This study has increased our understanding of some of the environmental drivers of the microalgae within the HRAP environment, which may assist with improving wastewater treatment and resource recovery., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity and CO2 augmentation is often used to overcome this limitation in summer. However, the implications of carbon limitation during winter are poorly understood. This paper investigates the effects of 0.5%, 2%, 5% and 10% CO2 addition on the winter-time performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, photosynthetic efficiency, biomass production and nutrient removal rates, along with community composition. Varying percentage CO2 addition and associated change in culture pH resulted in 3 distinct microalgal communities. Light absorption by the microalgae increased by up to 144% with CO2 addition, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. Carbon augmentation increased the maximum rate of photosynthesis by up to 172%, which led to increased microalgal biovolume by up to 181% and an increase in total organic biomass for all treatments except 10% CO2. While 10% CO2 improved light absorption and photosynthesis this did not translate to enhanced microalgal productivity. Increased microalgal productivity with CO2 addition did not result in increased dissolved nutrient (nitrogen and phosphorus) removal. This experiment demonstrated that winter-time carbon augmentation up to 5% CO2 improved microalgal light absorption and utilisation, which ultimately increased microalgal biomass and is likely to enhance total annual microalgal areal productivity in HRAPs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Recycling a portion of gravity harvested algae (i.e. algae and associated bacteria biomass) has been shown to improve both algal biomass productivity and harvest efficiency by maintaining the dominance of a rapidly-settleable colonial alga, Pediastrum boryanum in both pilot-scale wastewater treatment High Rate Algal Ponds (HRAP) and outdoor mesocosms. While algal recycling did not change the relative proportions of algae and bacteria in the HRAP culture, the contribution of the wastewater bacteria to the improved algal biomass productivity and settleability with the recycling was not certain and still required investigation. P. boryanum was therefore isolated from the HRAP and grown in pure culture on synthetic wastewater growth media under laboratory conditions. The influence of recycling on the productivity and settleability of the pure P. boryanum culture was then determined without wastewater bacteria present. Six 1 L P. boryanum cultures were grown over 30 days in a laboratory growth chamber simulating New Zealand summer conditions either with (Pr) or without (Pc) recycling of 10% of gravity harvested algae. The cultures with recycling (Pr) had higher algal productivity than the controls (Pc) when the cultures were operated at both 4 and 3 d hydraulic retention times by 11% and 38% respectively. Furthermore, algal recycling also improved 1 h settleability from ∼60% to ∼85% by increasing the average P. boryanum colony size due to the extended mean cell residence time and promoted formation of large algal bio-flocs (>500 μm diameter). These results demonstrate that the presence of wastewater bacteria was not necessary to improve algal productivity and settleability with algal recycling., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

With microalgal biofuels currently receiving much attention, there has been renewed interest in the combined use of high rate algal ponds (HRAP) for wastewater treatment and biofuel production. This combined use of HRAPs is considered to be an economically feasible option for biofuel production, however, increased microalgal productivity and nutrient removal together with reduced capital costs are needed before it can be commercially viable. Despite HRAPs being an established technology, microalgal photosynthesis and productivity is still limited in these ponds and is well below the theoretical maximum. This paper critically evaluates the parameters that limit microalgal light absorption and photosynthesis in wastewater HRAPs and examines biological, chemical and physical options for improving light absorption and utilisation, with the view of enhancing biomass production and nutrient removal., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The combined use of high rate algal ponds (HRAPs) for wastewater treatment and commercial algal production is considered to be an economically viable option. However, microalgal photosynthesis and biomass productivity is constrained in HRAPs due to light limitation. This paper investigates how the light climate in the HRAP can be modified through changes in pond depth, hydraulic retention time (HRT) and light/dark turnover rate and how this impacts light absorption and utilisation by the microalgae. Wastewater treatment HRAPs were operated at three different pond depth and HRT during autumn. Light absorption by the microalgae was most affected by HRT, significantly decreasing with increasing HRT, due to increased internal self-shading. Photosynthetic performance (as defined by Pmax, Ek and α), significantly increased with increasing pond depth and decreasing HRT. Despite this, increasing pond depth and/or HRT, resulted in decreased pond light climate and overall integrated water column net oxygen production. However, increased light/dark turnover was able to compensate for this decrease, bringing the net oxygen production in line with shallower ponds operated at shorter HRT. On overcast days, modelled daily net photosynthesis significantly increased with increased light/dark turnover, however, on clear days such increased turnover did not enhance photosynthesis. This study has showed that light absorption and photosynthetic performance of wastewater microalgae can be modified through changes to pond depth, HRT and light/dark turnover., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity, particularly in summer. This paper investigates the effects of CO₂ addition along a pH gradient on the performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, electron transport rate, photosynthetic efficiency, biomass production and nutrient removal efficiency. Light absorption by the microalgae increased by up to 128% with increasing CO₂ supply, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. CO₂ augmentation increased the maximum rate of both electron transport and photosynthesis by up to 256%. This led to increased biomass, with the highest yield occurring at the highest dissolved inorganic carbon/lowest pH combination tested (pH 6.5), with a doubling of chlorophyll-a (Chl-a) biomass while total microalgal biovolume increased by 660% in Micractinium bornhemiense and by 260% in Pediastrum boryanum dominated cultures. Increased microalgal biomass did not off-set the reduction in ammonia volatilisation in the control and overall nutrient removal was lower with CO₂ than without. Microalgal nutrient removal efficiency decreased as pH decreased and may have been related to decreased Chl-a per cell. This experiment demonstrated that CO₂ augmentation increased microalgal biomass in two distinct communities, however, care must be taken when interpreting results from standard biomass measurements with respect to CO₂ augmentation., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

When wastewater treatment high rate algal ponds (HRAP) are coupled with resource recovery processes, such as biofuel production, short hydraulic retention times (HRTs) are often favoured to increase the microalgal biomass productivity. However, short HRT can result in increased nutrient load to the HRAP which may negatively impact on the performance of the microalgae. This paper investigate the effects of high (NH4-N mean concentration 39.7 ± 17.9 g m(-3)) and moderate ((NH4-N mean concentration 19.9 ± 8.9 g m(-3)) nutrient loads and short HRT on the performance of microalgae with respect to light absorption, photosynthesis, biomass production and nutrient removal in pilot-scale (total volume 8 m(3)) wastewater treatment HRAPs. Microalgal biomass productivity was significantly higher under high nutrient loads, with a 133% and 126% increase in the chlorophyll-a and VSS areal productivities, respectively. Microalgae were more efficient at assimilating NH4-N from the wastewater under higher nutrient loads compared to moderate loads. Higher microalgal biomass with increased nutrient load resulted in increased light attenuation in the HRAP and lower light absorption efficiency by the microalgae. High nutrient loads also resulted in improved photosynthetic performance with significantly higher maximum rates of electron transport, oxygen production and quantum yield. This experiment demonstrated that microalgal productivity and nutrient removal efficiency were not inhibited by high nutrient loads, however, higher loads resulted in lower water quality in effluent discharge., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Laminar flows are a common problem in high rate algal ponds (HRAP) due to their long channels and gentle mixing by a single paddlewheel. Sustained laminar flows may modify the amount of light microalgal cells are exposed to, increase the boundary layer between the cell and the environment and increase settling out of cells onto the pond bottom. To date, there has been little focus on the effects of the time between mixing events (frequency of mixing) on the performance of microalgae in wastewater treatment HRAPs. This paper investigates the performance of three morphologically distinct microalgae in wastewater treatment high rate algal mesocosms operated at four different mixing frequencies (continuous, mixed every 45 min, mixed every 90 min and no mixing). Microalgal performance was measured in terms of biomass concentration, nutrient removal efficiency, light utilisation and photosynthetic performance. Microalgal biomass increased significantly with increasing mixing frequency for the two colonial species but did not differ for the single celled species. All three species were more efficient at NH4-N uptake as the frequency of mixing increased. Increased frequency of mixing supported larger colonies with improved harvest-ability by gravity but at the expense of efficient light absorption and maximum rate of photosynthesis. However, maximum quantum yield was highest in the continuously mixed cultures due to higher efficiency of photosynthesis under light limited conditions. Based on these results, higher microalgal productivity, improved wastewater treatment and better gravity based harvest-ability can be achieved with the inclusion of more mixing points and reduced laminar flows in full-scale HRAP., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The colonial alga Pediastrum boryanum has beneficial characteristics for wastewater treatment High Rate Algal Ponds (HRAP) including high biomass productivity and settleability. Our previous work has shown that these characteristics are enhanced when a portion of gravity harvested algae is recycled back to the pond. To help understand the mechanisms behind the improved performance of P. boryanum dominated HRAP with algal recycling, this study investigated the life-cycle of P. boryanum. Experiments determined the exact timing and growth rate of P. boryanum life-cycle stages ('juvenile', 'growth' and 'reproductive') under four combinations of light and temperature (250 or 120 μMol/m(2)/s; 20 or 10 °C). Single juvenile 16-celled colonies were grown in microcosms on an inverted microscope and photographed every 15 min until reproduction ceased. Two asexual life-cycles and a rarely occurring sexual life-cycle were observed. The time required to achieve asexual reproductive maturity increased from 52 h (high light and temperature) to 307 h (low light and temperature), indicating that the minimum hydraulic retention time or mean cell residence time (MCRT) must be higher than these values to sustain a P. boryanum HRAP culture under ambient conditions. The net growth rate of a P. boryanum colony varied between life-cycle stages (growth > juvenile > reproductive). This suggests that the higher biomass productivity measured in HRAP with algal recycling could be due to both the increased MCRT and an increase in the net growth rate of the HRAP culture by 'seeding' with faster growing colonies., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Depth has been widely recognised as a crucial operational feature of a high rate algal pond (HRAP) as it modifies the amount of light and frequency at which microalgal cells are exposed to optimal light. To date, there has been little focus on the optimisation of microalgal performance in wastewater treatment HRAPs with respect to depth, with advice ranging from as shallow as possible to 100 cm deep. This paper investigates the seasonal performance of microalgae in wastewater treatment HRAPs operated at three different depths (200, 300 and 400 mm). Microalgal performance was measured in terms of biomass production and areal productivity, nutrient removal efficiency and photosynthetic performance. The overall areal productivity significantly increased with increasing depth. Areal productivity ranged from 134 to 200% higher in the 400 mm deep HRAP compared to the 200 mm deep HRAP. Microalgae in the 400 mm deep HRAP were more efficient at NH4-N uptake and were photosynthetically more efficient compared to microalgae in the 200 mm deep HRAP. A higher chlorophyll-a concentration in the 200 mm deep HRAP resulted in a decrease in photosynthetic performance, due to insufficient carbon supply, over the course of the day in summer (as indicated by lower α, Pmax and oxygen production) compared to the 300 and 400 mm deep HRAPs. Based on these results, improved areal productivity and more wastewater can be treated per land area in the 400 mm deep HRAPs compared to 200 mm deep HRAPs without compromising wastewater treatment quality, while lowering capital and operational costs., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Recycling a portion of gravity harvested algae promoted the dominance of a rapidly settling colonial alga, Pediastrum boryanum (P. boryanum) and improved both biomass productivity and settleability in High Rate Algal Pond (HRAP) treating domestic wastewater. The effect of algal recycling rate on HRAP performance was investigated using 12 replicate mesocosms (18 L) that were operated semi-continuously under ambient conditions. Three experiments were conducted during different seasons with each experiment lasting up to 36 days. Recycling 10%, 25%, and 50% of the 'mass' of daily algal production all increased total biomass concentration in the mesocosms. However, recycling >10% reduced the organic content (volatile suspended solids (VSS)) of the mesocosm biomass from 83% to 68% and did not further increase biomass productivity (based on VSS). This indicates that if a HRAP is operated with a low algal concentration and does not utilise all the available sunlight, algal recycling increases the algal concentration up to an optimum level, resulting in higher algal biomass productivity. Recycling 10% of the daily algal production not only increased biomass productivity by ∼40%, but increased biomass settleability by ∼25%, which was probably a consequence of the ∼30% increase in P. boryanum dominance in the mesocosms compared with controls without recycling.

It has previously been shown that recycling gravity harvested algae promotes Pediastrum boryanum dominance and improves harvestability and biomass production in pilot-scale High Rate Algal Ponds (HRAPs) treating domestic wastewater. In order to confirm the reproducibility of these findings and investigate the mechanisms responsible, this study utilized twelve 20 L outdoor HRAP mesocosms operated with and without algal recycling. It then compared the recycling of separated solid and liquid components of the harvested biomass against un-separated biomass. The work confirmed that algal recycling promoted P. boryanum dominance, improved 1 h-settleability by >20% and increased biomass productivity by >25% compared with controls that had no recycling. With regard to the improved harvestability, of particular interest was that recycling the liquid fraction alone caused a similar improvement in settleability as recycling the solid fraction. This may be due to the presence of extracellular polymeric substances in the liquid fraction. While there are many possible mechanisms that could account for the increased productivity with algal recycling, all but two were systematically eliminated: (i) the mean cell residence time was extended thereby increasing the algal concentration and more fully utilizing the incident sunlight and, (ii) the relative proportions of algal growth stages (which have different specific growth rates) was changed, resulting in a net increase in the overall growth rate of the culture., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This paper investigates the effect of recycling on biomass energy yield in High Rate Algal Ponds (HRAPs). Two 8 m(3) pilot-scale HRAPs treating primary settled sewage were operated in parallel and monitored over a 2-year period. Volatile suspended solids were measured from both HRAPs and their gravity settlers to determine biomass productivity and harvest efficiency. The energy content of the biomass was also measured. Multiplying biomass productivity and harvest efficiency gives the 'harvestable biomass productivity' and multiplying this by the energy content defines the actual 'biomass energy yield'. In Year 1, algal recycling was implemented in one of the ponds (HRAPr) and improved harvestable biomass productivity by 58% compared with the control (HRAPc) without recycling (HRAPr: 9.2 g/m(2)/d; HRAPc: 5.8 g/m(2)/d). The energy content of the biomass grown in HRAPr, which was dominated by Pediastrun boryanum, was 25% higher than the control HRAPc which contained a mixed culture of 4-5 different algae (HRAPr: 21.5 kJ/g; HRAPc: 18.6 kJ/g). In Year 2, HRAPc was then seeded with the biomass harvested from the P. boryanum dominated HRAPr. This had the effect of shifting algal dominance from 89% Dictyosphaerium sp. (which is poorly-settleable) to over 90% P. boryanum in 5 months. Operation of this pond was then switched to recycling its own harvested biomass, which maintained P. boryanum dominance for the rest of Year 2. This result confirms, for the first time in the literature, that species control is possible for similarly sized co-occurring algal colonies in outdoor HRAP by algal recycling. With regard to the overall improvement in biomass energy yield, which is a critical parameter in the context of algal cultivation for biofuels, the combined improvements that recycling triggered in biomass productivity, harvest efficiency and energy content enhanced the harvested biomass energy yield by 66% (HRAPr: 195 kJ/m(2)/day; HRAPc: 118 kJ/m(2)/day)., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

We implemented the IWA River Water Quality Model No. 1 (Reichert et al., 2001. River Water Quality Model No. 1, IWA Scientific & Technical Report No. 12) to simulate water-quality characteristics in two pilot-scale High Rate Algal Ponds. Simulation results were compared with two years' of data from the ponds. The first year's data from one pond were used for model calibration; the remaining data were used for validation. As originally formulated and parameterized, the model consistently yielded summer-time algal biomass concentrations which were too low - with consequent failures in its reproduction of dissolved oxygen, pH and nutrient dynamics. We experimented with various structural/parametric changes to improve the model's performance. The most effective strategy was to greatly increase the respiratory losses suffered by the heterotrophic osmotrophs (thereby giving the algae access to a larger fraction of the incoming dissolved organic carbon and nitrogen). This suggests that CO(2)-bubbling alone cannot entirely preclude resource-limitation of algal production. We doubt that our parameterization of heterotrophic osmotrophs is correct and infer that the algae derive a large fraction of their nutrition by direct osmotrophic uptake of dissolved organic matter. This inference is supported by the literature concerning the physiology of the dominant algal species in our ponds., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

This paper investigates the influence of recycling gravity harvested algae on species dominance and harvest efficiency in wastewater treatment High Rate Algal Ponds (HRAP). Two identical pilot-scale HRAPs were operated over one year either with (HRAP(r)) or without (HRAP(c)) harvested algal biomass recycling. Algae were harvested from the HRAP effluent in algal settling cones (ASCs) and harvest efficiency was compared to settlability in Imhoff cones five times a week. A microscopic image analysis technique was developed to determine relative algal dominance based on biovolume and was conducted once a month. Recycling of harvested algal biomass back to the HRAP(r) maintained the dominance of a single readily settleable algal species (Pediastrum sp.) at >90% over one year (compared to the control with only 53%). Increased dominance of Pediastrum sp. greatly improved the efficiency of algal harvest (annual average of >85% harvest for the HRAP(r) compared with ∼60% for the control). Imhoff cone experiments demonstrated that algal settleability was influenced by both the dominance of Pediastrum sp. and the species composition of remaining algae. Algal biomass recycling increased the average size of Pediastrum sp. colonies by 13-30% by increasing mean cell residence time. These results indicate that recycling gravity harvested algae could be a simple and effective operational strategy to maintain the dominance of readily settleable algal species, and enhance algal harvest by gravity sedimentation., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

While temperature is fundamental to the design and optimal operation of shallow algal ponds, there is currently no temperature model universally applicable to these systems. This paper presents a model valid for any opaque water body of uniform temperature profile. This new universal model was tested against 1 year of experimental data collected from a wastewater treatment high rate algal pond. On the basis of 1 year of data collected every 15 min, the average errors of the predicted afternoon peak and predawn minimum were both only 1.3 °C and the average error between these extremes was just 1.2 °C. In order to demonstrate the improvement in accuracy gained, the expressions for heat fluxes used in nine prior temperature models were systematically substituted into the new universal model and evaluated against the experimental data. Errors in the peak and minimum temperatures increased by up to 2.1 and 3.2 °C, respectively, while the error between these extremes increased by up to 2.9 °C. In practical applications, these levels of inaccuracies could lead to an under/overestimation of the algal productivity and the evaporative water loss by approximately 40% and 300%, respectively.

This paper examines the potential of algae biofuel production in conjunction with wastewater treatment. Current technology for algal wastewater treatment uses facultative ponds, however, these ponds have low productivity (∼10 tonnes/ha.y), are not amenable to cultivating single algal species, require chemical flocculation or other expensive processes for algal harvest, and do not provide consistent nutrient removal. Shallow, paddlewheel-mixed high rate algal ponds (HRAPs) have much higher productivities (∼30 tonnes/ha.y) and promote bioflocculation settling which may provide low-cost algal harvest. Moreover, HRAP algae are carbon-limited and daytime addition of CO(2) has, under suitable climatic conditions, the potential to double production (to ∼60 tonnes/ha.y), improve bioflocculation algal harvest, and enhance wastewater nutrient removal. Algae biofuels (e.g. biogas, ethanol, biodiesel and crude bio-oil), could be produced from the algae harvested from wastewater HRAPs, The wastewater treatment function would cover the capital and operation costs of algal production, with biofuel and recovered nutrient fertilizer being by-products. Greenhouse gas abatement results from both the production of the biofuels and the savings in energy consumption compared to electromechanical treatment processes. However, to achieve these benefits, further research is required, particularly the large-scale demonstration of wastewater treatment HRAP algal production and harvest.

Wastewater treatment High Rate Algal Ponds with CO2 addition could provide cost-effective and efficient tertiary-level wastewater treatment with the co-benefit of algal biomass production for biofuel use. Wastewater grown algal biomass can have a lipid content of 10-30% of dry weight, which could be used to make biodiesel. This research investigated algal biomass and total lipid production by two pilot-scale wastewater treatment HRAP(S) (4-day HRT) with and without CO2 addition under New Zealand mid summer (Nov-Jan) conditions. The influence of CO2 addition on wastewater treatment performance was also determined. CO2 was added to one of the HRAPs (the HRAP(E)) by maintaining the maximum pH of the pond below 8. Measurements of HRAP influent and effluent water qualities, total lipid content and algal biomass production were made twice a week over the experimental period. Both HRAP(S) achieved high levels of organic compound and nutrient removal, with >85% SBOD5, >92 NH4(+)-N and >70% DRP removal. Algal/bacterial biomass production in the HRAP(E) (15.2 g/m2/d) was improved by CO2 addition by approximately 30% compared with that of the control HRAP(W) (10.6 g/m2/d). Total lipid content of the biomass grown on both HRAP(S) was slightly reduced (from 25% to 20%) with CO2 addition and the maximum total lipid content of approximately 40% was observed in the HRAP(W) when low NH4(+)-N concentration (<0.5 mg/L) and high maximum pH (>10.0) occurred. Total lipid content of the biomass increased by approximately 15% under nitrogen limiting conditions, however, overall algal/bacterial biomass production was reduced by half during the period of nitrogen limitation. More research is required to maintain algal production under near nitrogen-limiting conditions.

While research and development of algal biofuels are currently receiving much interest and funding, they are still not commercially viable at today's fossil fuel prices. However, a niche opportunity may exist where algae are grown as a by-product of high rate algal ponds (HRAPs) operated for wastewater treatment. In addition to significantly better economics, algal biofuel production from wastewater treatment HRAPs has a much smaller environmental footprint compared to commercial algal production HRAPs which consume freshwater and fertilisers. In this paper the critical parameters that limit algal cultivation, production and harvest are reviewed and practical options that may enhance the net harvestable algal production from wastewater treatment HRAPs including CO(2) addition, species control, control of grazers and parasites and bioflocculation are discussed., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Algae are produced in considerable quantities in oxidation ponds, and may negatively affect receiving waters when discharged at high concentration. Thus in some instances they require removal prior to effluent discharge, which may be enhanced using flocculants such as alum. Harvested algal biomass could be anaerobically digested to methane for use as a renewable energy source, however, alum, has been reported to inhibit anaerobic digestion. Psychrophilic (20°C) anaerobic digestion experiments showed a 13% reduction in methane production with 200 g m(-3) alum in the flocculated algae, and a 40% reduction at an alum concentration of 1600 g m(-3). Elevated ammoniacal-N concentrations (785 g NH(4)(+)-N m(-3)) also inhibited algal digestion at 20°C when using an inoculum of anaerobic bacteria from a mesophylic municipal wastewater sludge digester. However, anaerobic digestion using a bacterial inoculum from a psychrophilic piggery anaerobic pond (in which typical ammoniacal-N levels range between 200 and 2000 g NH(4)(+)-N m(-3)) were unaffected by elevated digester ammoniacal-N levels and methane production actually increased slightly at higher ammoniacal-N concentrations. Thus, selecting an anaerobic bacterial inoculum that is already adapted to high ammoniacal-N levels and the digestion temperature, such as that form an anaerobic pond treating piggery wastewater, may avoid ammonia inhibition of algal digestion.

The influence of CO2 addition to high rate algal ponds (HRAPS) on nitrogen removal was investigated using two pilot-scale HRAPs operated with different hydraulic retention times (HRT: 4 and 8 days), and was compared to the nitrogen removal by the 8-day HRT pond before CO2 addition was installed. Nitrogen balances were calculated by partitioning total nitrogen into organic and inorganic nitrogen (NH4+-N and NO3--N), and by separation of the organic nitrogen into particulate (PON) and dissolved organic nitrogen (DON). PON was further divided into algal organic nitrogen (AON) and bacteria organic nitrogen (BON) to investigate nitrogen mass flow in the HRAPS. This research shows that the proportion of algae in the algal/bacterial biomass in the longer 8-day HRT HRAP8d (55.6%) was appreciably lower than that in the shorter 4-day HRT HRAP4d (80.5%) when CO2 was added to control the maximum pH to <8.0 during the summer. Higher bacterial biomass in the longer 8-day HRT HRAP corresponded with higher nitrification rates, indicating that the longer 8-day HRT in the summer was detrimental for two reasons: lower algal productivity and increased nitrogen loss through nitrification/denitrification. Overall nitrogen removal of approximately 60% in the HRAPS with CO2 addition was mainly achieved by algal assimilation followed by sedimentation in the settling unit.

High rate algal ponds (HRAPs) provide improved wastewater treatment over conventional wastewater stabilisation ponds; however, algal production and recovery of wastewater nutrients as algal biomass is limited by the low carbon:nitrogen ratio of wastewater. This paper investigates the influence of CO(2) addition (to augment daytime carbon availability) on wastewater treatment performance and algal production of two pilot-scale HRAPs operated with different hydraulic retention times (4 and 8 days) over a New Zealand Summer (November-March, 07/08). Weekly measurements were made of influent and effluent flow rate and water qualities, algal and bacterial biomass production, and the percentage of algae biomass harvested in gravity settling units. This research shows that the wastewater treatment HRAPs with CO(2) addition achieved a mean algal productivity of 16.7 g/m(2)/d for the HRAP(4d) (4 d HRT, maximum algae productivity of 24.7 g/m(2)/d measured in January 08) and 9.0 g/m(2)/d for the HRAP(8d) (8 d HRT)). Algae biomass produced in the HRAPs was efficiently harvested by simple gravity settling units (mean harvested algal productivity: 11.5 g/m(2)/d for the HRAP(4d) and 7.5 g/m(2)/d for the HRAP(8d) respectively). Higher bacterial composition and the larger size of algal/bacterial flocs of the HRAP(8d) biomass increased harvestability (83%) compared to that of HRAP(4d) biomass (69%).

New Zealand has over 1000 anaerobic waste stabilisation ponds treating wastewater from farms and industry. Traditional anaerobic ponds were not designed to optimise anaerobic digestion to produce biogas and are therefore uncovered, releasing biogas to the atmosphere, which can cause odour problems and contributes to GHG emissions. The biogas production and treatment performance of an anaerobic piggery pond retrofitted with a perimeter cover working under field conditions was monitored over a 14 month period. The cover design proved successful in capturing biogas, mitigating odour and GHG issues and coping with New Zealand weather conditions. High solids removal rates (73% and 86% for TS and VS respectively) were achieved. An annual average biogas methane production rate of 0.263 m(3) CH(4)/kgVS(added) was observed, which is similar to gas production rates of mesophilic farm waste digesters, and indicates that the prolonged hydraulic and solids retention times of covered anaerobic ponds can fully compensate for lower operating temperatures. These results suggest that covered anaerobic ponds treating agricultural wastes in New Zealand have great potential to reduce odour and GHG emissions and recover renewable energy, while producing an easy to handle effluent for land irrigation or further treatment.

A laboratory-scale hybrid-denitrification filter (HDF) was designed by combining a plant material digester and a denitrification filter into a single unit for the removal of nitrate and phosphorus from glasshouse hydroponic wastewater. The carbon to nitrate (C:N) ratio for efficient operation of the HDF was calculated to be 1.93:1 and the COD/BOD(5) ratio was 1.2:1. When the HDF was continuously operated with the plant material replaced every 2 days and 100% internal recirculation of the effluent, a high level of nitrate removal (320-5 mg N/L, >95% removal) combined with a low effluent sBOD(5) concentration (<5mg/L) was consistently achieved. Moreover, phosphate concentrations in the effluent were maintained below 7.5 mg P/L (>81% reduction). This study demonstrates the potential to combine a digester and a denitrification filter in a single unit to efficiently remove nitrate and phosphate from hydroponic wastewater in a single unit.

This study investigated the feasibility of using pre-treated plant liquors as organic carbon sources for the treatment of hydroponic wastewater containing high nitrate-N (>300 mg N/L). The waste plant material was pre-treated to extract organic carbon-rich liquors. When this plant liquor was used as an organic carbon source in denitrification filters at the organic carbon:nitrogen dose rate of 3C:N, nitrate removal efficiencies were >95% and final effluent nitrate concentrations were consistently <20mg N/L. However, at this dose rate, relatively high concentrations (>140 mg/L) of organic carbon (fBOD5) remained in the final effluents. Therefore, a 'compromise' organic carbon:nitrogen dose rate (2C:N) was trialled, at which nitrate removal efficiencies were maintained at >85%, final effluent nitrate concentrations were consistently below 45 mg N/L, and effluent fBOD5 concentrations were <25mg/L. This study has demonstrated that waste plant material is a suitable carbon source for the removal of nitrate from hydroponic wastewater in a denitrification filter.

Biogas produced by anaerobic treatment of wastewater can be collected and used for power generation. However, the biogas may require scrubbing to prevent corrosion by H2S and to improve engine efficiency by reducing the CO2 content. HRAP can be used to scrub biogas during the daytime when they are carbon-limited and have high pH. This study investigates the influence of the carbon dioxide addition from biogas scrubbing on high rate algal pond wastewater treatment performance (in terms of BOD, NH4-N, DRP and E. coli removal) and algal production (growth and species composition). Batch culture experiments were conducted in laboratory microcosms (2 L) and outside mesocosms (20 L). Results indicate that CO2 addition and reduced culture pH increased algal production and nutrient assimilation, decreased high pH mediated nutrient removal processes (phosphate precipitation and ammonia volatilisation), but had little influence on the ability of the culture to remove filtered BODs. Disinfection, as indicated by E.coli removal; was reduced, however, further research on virus removal, which is not affected by culture pH, is required. These preliminary findings indicate the potential to scrub C02 from biogas using high rate pond water without decreasing the effectiveness of wastewater treatment and enabling increased recovery of wastewater nutrients as algal biomass.

New Zealand has over 1000 anaerobic wastewater stabilisation ponds used for the treatment of wastewater from farms and industry. Traditional anaerobic ponds were not designed to optimise anaerobic digestion of wastewater biomass to produce biogas and these uncovered ponds allowed biogas to escape to the atmosphere. This release of biogas not only causes odour problems, but contributes to GHG (greenhouse gas) emissions and is wasteful of energy that could be captured and used. Biogas production from anaerobic stabilisation ponds treating piggery and dairy wastewater was measured using floating 25 m2 HDPE covers on the pond surface. Biogas composition was analysed monthly and gas production was continually monitored. Mean areal biogas (methane) production rates from piggery and dairy anaerobic ponds were 0.78 (0.53) m3/m2/d and 0.03 (0.023) m3/m2/d respectively. Average CH4 content of the piggery and dairy farm biogas were 72.0% and 80.3% respectively. Conversion of the average volume of methane gas that could be captured from the piggery and dairy farm ponds (393.4 m3/d and 40.7 m3/d) to electricity would reduce CO2 equivalent GHG emissions by 5.6 tonnes/d and 0.6 tonnes/d and generate 1,180 kWh/d and 122 kWh/d. These results suggest that anaerobic ponds in New Zealand release considerable amounts of GHG and that there is great potential for energy recovery.

Advanced pond systems (APS), incorporating high-rate ponds, algal settling ponds, and maturation ponds, typically achieve better and more consistent disinfection as indicated by Escherichia coli than conventional waste stabilisation ponds. To see whether this superior disinfection extends also to enteric viruses, we studied the removal of somatic phages ('model' viruses) in a pilot-scale APS treating sewage. Measurements through the three aerobic stages of the APS showed fairly good removal of somatic phage in the summer months (2.2 log reduction), but much less effective removal in winter (0.45 log reduction), whereas E. coli was removed efficiently (> 4 logs) in both seasons. A very steep depth-gradient of sunlight inactivation of somatic phage in APS pond waters (confined in silica test tubes) is consistent with inactivation mainly by solar UVB wavelengths. Data for F-RNA phage suggests involvement of longer UV wavelengths. These findings imply that efficiency of virus removal in APS will vary seasonally with variation in solar UV radiation.

The treatment performance of a maturation pond (MP), the typical final polishing stage of an Advanced Pond System (APS), is compared with that of a surface-flow constructed wetland (CW) over 19 months. Both received approximately 67 mm d-1 of wastewater after passage through upstream stages of the APS. The MP, with greater sunlight exposure, had higher algal biomass (and associated suspended solids) than the CW, showed higher dissolved oxygen (DO) concentrations and greater diurnal variation in DO and pH. Neither polishing stages reduced nutrients markedly, with the CW exporting slightly more NH(3)-N and DRP, and less NO(3)-N than the MP. Disinfection was more efficient in the MP (geometric mean 1 log load removal, 12 MPN (100ml)-1) compared to the CW (0.47 log load removal, 53 MPN (100ml)-1). Incorporation of a final rock filter (28% of area) reduced median solids levels to < 10 g m(-3) in both the MP and CW. A hybrid between MPs and CWs with alternating zones of open-water (for enhanced disinfection and zooplankton grazing of algal solids) and wetland vegetation (promoting sedimentation and denitrification, and providing refugia for zooplankton) may provide more consistent effluent quality that either stage alone.

The optical character of waste stabilization ponds (WSPs) is of concern for several reasons. Algal photosynthesis, which produces oxygen for waste oxidation in WSPs, is influenced by attenuation of sunlight in ponds. Disinfection in WSPs is influenced by optical characteristics because solar UV exposure usually dominates inactivation. The optical nature of WSPs effluent also affects assimilation by receiving waters. Despite the importance of light behaviour in WSPs, few studies have been made of their optical characteristics. We discuss simple optical measures suitable for routine monitoring of WSPs (including at sites remote from laboratories): optical density of filtrates - an index of dissolved coloured organic (humic) matter, visual clarity - to provide an estimate of the beam attenuation coefficient (a fundamental quantity needed for optical modelling) colour (hue) - as an indicator of general WSP 'condition' and irradiance attenuation quantifying depth of light penetration. The value of optical characterisation of WSPs is illustrated with reference to optical data for WSPs in NZ (including high-rate algal ponds) treating dairy cattle wastewater versus domestic sewage. We encourage increased research on optical characteristics of WSPs and the incorporation of optical measures in monitoring and modelling of WSP performance.

Many domestic Wastewater Stabilisation Ponds (WSPs) or oxidation ponds in New Zealand require upgrading to reduce pollution of receiving waters. Advanced Pond Systems (APS) consisting of an Advanced Facultative Pond, High Rate Pond, Algae Settling Pond and Maturation Pond may provide a cost effective upgrade option. This paper presents the results of a 2-year study of the performance of two pilot APS systems with High Rate Ponds of different depths and areas. The HRPs of the APS systems both had the same flow rate (5 m3 d(-1)), volume (37.5 m3) and thus hydraulic retention time (7.5 d). However, the East HRP had an operating depth of 0.30 m and a surface area of 128 m2, and the West HRP had an operating depth of 0.45 m and a surface area of 85 m2. APS system performance was compared in terms of improvement of water quality. For nearly all parameters measured, there was little difference in performance between the two systems suggesting that the system with the smaller area could be used without affecting treatment. Comparison of final effluent with typical effluent of New Zealand WSPs showed that APS effluent was of higher quality and much less variable over time.

New Zealand has 16,500 dairy farms (avg. 220 cows), with cows kept on pasture throughout the year. During the 9-month dairy season, the cows are milked twice a day (averaging 2.5-3 h per day in the dairy parlour). Urine and faecal wastes deposited in the dairy parlour are washed away with high pressure hoses, using large volumes of water. A common method of treatment is in simple two-pond (anaerobic/facultative) lagoon systems, which remove about 95% of suspended solids and BOD5, but only 75% of total-N prior to discharge. High concentrations of ammoniacal-N in the effluent can cause toxicity to aquatic organisms in receiving waters. Mechanical aeration of the second (facultative) lagoon to promote nitrification improves effluent quality by reducing oxygen demand and potential ammonia toxicity to streamlife. Mechanical aeration however is associated with considerable mixing, which may prevent algae from optimising photosynthesis in the facultative lagoon. A series of experiments was undertaken which tested the efficiency of mechanical aeration and then attempted to combine it with daytime algal oxygen production in order to maximise ammonia conversion to nitrate, while minimising costs to the farmer. An experimental facility was developed by dividing a large facultative lagoon into two, producing a matched pair of lagoons, operated in parallel with influent flow split equally. Over successive dairy seasons, various aeration regimes were compared. Continuous aeration promoted nearly complete nitrification of the ammoniacal-N (99% removal), and effluent BOD was approximately halved. However the continuous mixing reduced algal biomass, and thus daytime algal photosynthesis. Night-only aeration permitted greater algal photosynthesis to occur, as well as halving electrical power consumption. Ammoniacal-N removal reduced to 90% (10 g m(-3) remaining in the effluent), while BOD removal was also lower than in the continuously aerated lagoon (59 and 69% respectively). Providing a series of biofilm attachment surfaces for nitrifying bacteria by suspending geotextile material close to the surface in the pond in consistently aerobic water resulted in improved ammoniacal-N removal efficiency (93%) with night aeration, but still lower removal than continuous aeration.

Waste stabilisation ponds (WSPs) have been used for the treatment of dairy farm wastewater in New Zealand since the 1970s. The conventional two pond WSP systems provide efficient removal of wastewater BOD5 and total suspended solids, but effluent concentrations of other pollutants including nutrients and faecal bacteria are now considered unsuitable for discharge to waterways. Advanced Pond Systems (APS) provide a potential solution. A pilot dairy farm APS consisting of an Anaerobic pond (the first pond of the conventional WSP system) followed by three ponds: a High Rate Pond (HRP), an Algae Settling Pond (ASP) and a Maturation Pond (which all replace the conventional WSP system facultative pond) was evaluated over a two year period. Performance was compared to that of the existing conventional dairy farm WSP system. APS system effluent quality was considerably higher than that of the conventional WSP system with respective median effluent concentrations of BOD5: 34 and 108 g m(-3), TSS: 64 and 220 g m(-3), NH4-N: 8 and 29 g m(-3), DRP: 13 and 17 g m(-3), and E. coli: 146 and 16195 MPN/100 ml. APS systems show great promise for upgrading conventional dairy farm WSPs in New Zealand.

"Advanced" pond systems (APS) have the potential for improving treatment, including disinfection, over conventional WSPs. Disinfection in a pilot scale APS at Ngatea, New Zealand was studied. This system comprises a high-rate algal pond (HRP) that optimises growth of settleable colonial green algae, followed by an algal settling pond (ASP) that removes much of the nutrients and solids as non-noxious algal sludge, and then a maturation pond (MP) for effluent polishing. Monitoring of this pilot-scale system over 2 years showed excellent overall removal of E. coli (average of 2000-fold reduction), with approximately 1 log removal in each of the three stages. Experiments in the pilot scale HRP suggest that most E. coli removal in this stage is inactivation by sunlight exposure, but with an important contribution from continuous dark processes. Preliminary experiments on the pilot scale algal settling pond (APS) suggest the combined effect of sedimentation of bacteria and sunlight disinfection of the (clarified) supernatant water.

Algal turf scrubbing (ATS) is a novel wetland technology that has been designed and engineered to promote natural wastewater treatment processes. Algal turf scrubbing improves water quality by passing a shallow stream of wastewater over the surface of a gently sloped floway. The floway is colonised by a natural heterogeneous assemblage of periphyton consisting of cyanobacteria, filamentous algae and epiphytic diatoms together with aerobic bacteria and fungi. Algal photosynthesis provides oxygen for aerobic breakdown of wastewater by heterotrophic bacteria. Pollutants are extracted from the wastewater by several processes including assimilation, adsorption, filtration and precipitation. The algal turf is harvested periodically to remove the accumulated periphyton biomass and associated pollutants from the system. This paper will present results from a demonstration ATS facility in Patterson, California which was used to polish secondarily treated wastewater. The design and operational factors that influence the treatment performance of ATS systems is discussed. Results indicate the potential of the ATS for nutrient removal from secondarily treated wastewater and agricultural drainage waters.