A series of eight experiments were carried out to analyse the effects of light intensity, light duration and photoperiods on a microalgae culture for treating AnMBR effluent at an outdoor photobioreactor (PBR) plant.Improved performance was achieved in terms of nutrient recovery rates, biomass productivity and effluent nutrient concentrations at a higher net photon flux. However, the higher irradiance was also responsible for lower biomass productivity:light irradiance ratios.None of the experiments with different lighting regimes and the same net photon flux showed any significant differences. The data obtained suggest that microalgae performance in this system did not depend on the time of day when light was applied or the length of the photoperiods, but on the net photon flux. No photoinhibiton was * Constant energy consumption of 0.8 KwhSolar light is the most economical option for outdoor microalgae cultivation [24,39], but variations in the weather, day:night cycles and seasonal changes affect light intensity

With the aim of assessing the potential of microalgae cultivation for water resource recovery (WRR), the performance of three 0.55m(3) flat-plate photobioreactors (PBRs) was evaluated in terms of nutrient removal rate (NRR) and biomass production. The PBRs were operated outdoor (at ambient temperature and light intensity) using as growth media the nutrient-rich effluent from an AnMBR fed with pre-treated sewage. Solar irradiance was the most determining factor affecting NRR. Biomass productivity was significantly affected by temperatures below 20°C. The maximum biomass productivity (52.3mgVSS·L(-1)·d(-1)) and NRR (5.84mgNH4-N·L(-1)·d(-1) and 0.85mgPO4-P·L(-1)·d(-1)) were achieved at solar irradiance of 395μE·m(-2)·s(-1), temperature of 25.5°C, and HRT of 8days. Under these conditions, it was possible to comply with effluent nutrient standards (European Directive 91/271/CEE) when the nutrient content in the influent was in the range of 40-50mgN·L(-1) and 6-7mg P·L(-1).

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The objective of this work was to evaluate the performance of a pilot scale membrane photobioreactor (MPBR) for treating the effluent of an anaerobic membrane bioreactor (AnMBR) system. In particular, new experimental data on microalgae productivity, nutrient recovery, CO2 biofixation and energy recovery potential was obtained under different operating conditions, which would facilitate moving towards cost-effective microalgae cultivation on wastewater. To this aim, a 2.2-m 3 MPBR equipped with two commercial-scale hollow-fibre ultrafiltration membrane modules was operated treating the nutrientloaded effluent from an AnMBR for sewage treatment. The influence of several design, environmental and operating parameters on MPBR performance was studied. Among the conditions evaluated, variations in solar irradiance significantly affected the nutrient recovery rate (NRR). Operating at temperatures above 25 ºC and high biomass concentrations, which increased light shading effect, negatively affected biomass production and NRR. Maximum biomass productivity of 66 mg VSS•L-1 •d-1 2 (areal productivity of 15.78 g VSS•m-2 •d-1) and NRR of 7.68 mg N•L-1 •d-1 and 1.17 mg P•L-1 •d-1 were achieved when operating at 4.5 days of biomass retention time. These results would outcome maximum theoretical energy recoveries and CO2 biofixations of about 0.43 kWh and 0.51 kg CO2 per m 3 of treated water, respectively. Moreover, the excellent quality permeate that was produced (i.e. negligible levels of pathogens and suspended solids) represents a reclaimed water source.

Microalgae cultivation appears to be a promising technology for treating nutrient-rich effluents from anaerobic membrane bioreactors, as microalgae are able to consume nutrients from sewage without an organic carbon source, although the sulphide formed during the anaerobic treatment does have negative effects on microalgae growth. Short and long-term experiments were carried out on the effects of sulphide on a mixed microalgae culture. The short-term experiments showed that the oxygen production rate (OPR) dropped as sulphide concentration increased: a concentration of 5mgSL reduced OPR by 43%, while a concentration of 50mgSL came close to completely inhibiting microalgae growth. The long-term experiments revealed that the presence of sulphide in the influent had inhibitory effects at sulphide concentrations above 20mgSL in the culture, but not at concentrations below 5mgSL. These conditions favoured Chlorella growth over that of Scenedesmus.