Algal-based, single-step treatment of urban wastewaters.

Currently, urban wastewaters (UWW) laden with organic carbon (BOD) and nutrients (ammoniacal nitrogen, N, and phosphates, P) are treated in multi-stage, energy-intensive process trains to meet the mandated discharge standards. This study presents a single-step process based on mixotrophic metabolism for simultaneous removal of carbon and nutrients from UWWs. The proposed system is designed specifically for hot, arid environments utilizing an acidophilic, thermotolerant algal species, Galdieria sulphuraria, and an enclosed photobioreactor to limit evaporation. Removal rates of BOD, N, and P recorded in this study (14.93, 7.23, and 1.38 mg L(-1) d(-1), respectively) are comparable to literature reports. These results confirm that the mixotrophic system can reduce the energy costs associated with oxygen supply in current UWW treatment systems, and has the potential to generate more energy-rich biomass for net energy extraction from UWW.

Algal biofuels from urban wastewaters: maximizing biomass yield using nutrients recycled from hydrothermal processing of biomass.

Recent studies have proposed algal cultivation in urban wastewaters for the dual purpose of waste treatment and bioenergy production from the resulting biomass. This study proposes an enhancement to this approach that integrates cultivation of an acidophilic strain, Galdieria sulphuraria 5587.1, in a closed photobioreactor (PBR); hydrothermal liquefaction (HTL) of the wet algal biomass; and recirculation of the nutrient-rich aqueous product (AP) of HTL to the PBR to achieve higher biomass productivity than that could be achieved with raw wastewater. The premise is that recycling nutrients in the AP can maintain optimal C, N and P levels in the PBR to maximize biomass growth to increase energy returns. Growth studies on the test species validated growth on AP derived from HTL at temperatures from 180 to 300°C. Doubling N and P concentrations over normal levels in wastewater resulted in biomass productivity gains of 20-25% while N and P removal rates also doubled.

Evaluation of a thermo-tolerant acidophilic alga, Galdieria sulphuraria, for nutrient removal from urban wastewaters.

Nutrient removal from primary wastewater effluent was tested using Galdieria sulphuraria, an acidophilic and moderately thermophilic alga. Biomass yield recorded in this study (27.42g biomass per g nitrogen removed) is higher than the average reported in the literature (25.75g g(-1)) while, the theoretical yield estimated from the empirical molecular formula of algal biomass is 15.8g g(-1). Seven-day removal efficiencies were 88.3% for ammoniacal-nitrogen and 95.5% for phosphates; corresponding removal rates were 4.85 and 1.21mg L(-1)d(-1). Although these rates are lower than the average literature values for other strains (6.36 and 1.34mg L(-1)d(-1), respectively), potential advantages of G. sulphuraria for accomplishing energy-positive nutrient removal are highlighted. Feasibility of growing G. sulphuraria outdoors at densities higher than in high-rate oxidation ponds is also demonstrated.