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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.)