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Yuan X.,University of Massachusetts Amherst | Kumar A.,Pollution Prevention and Control Core | Sahu A.K.,Aquateam Norwegian Water Technology Center | Ergas S.J.,University of South Florida
Bioresource Technology | Year: 2011

Spirulina platensis was cultivated in a bench-scale airlift photobioreactor using synthetic wastewater (total nitrogen 412mgL-1, total phosphorous 90mgL-1, pH 9-10) with varying ammonia/total nitrogen ratios (50-100% ammonia with balance nitrate) and hydraulic residence times (15-25d). High average biomass density (3500-3800mgL-1) and productivity (5.1gm-2d-1) were achieved when ammonia was maintained at 50% of the total nitrogen. Both high ammonia concentrations and mutual self-shading, which resulted from the high biomass density in the airlift reactor, were found to partially inhibit the growth of S. platensis. The performance of the airlift bioreactor used in this study compared favorably with other published studies. The system has good potential for treatment of high strength wastewater combined with production of algae for biofuels or other products, such as human and animal food, food supplements or pharmaceuticals. © 2010 Elsevier Ltd.

Rusten B.,Aquateam Norwegian Water Technology Center | Sahu A.K.,Aquateam Norwegian Water Technology Center
Water Science and Technology | Year: 2011

Proof-of-concept has been demonstrated for a process that will utilize nutrients from sludge liquor, natural light, and CO 2 from biogas to grow microalgae at wastewater treatment plants. This process will reduce the impact of returning side-streams to the head of the plant. The produced algae will be fed to anaerobic digesters for increased biogas production. Dewatering of anaerobically digested sludge in centrifuges produces reject water with extremely low transmittance of light. A pre-treatment procedure was developed that improved light transmittance for reject water from the FREVAR, Norway, wastewater treatment plant from 0.1% T to 77% T (670 nm, 1 cm path). Chlorella sp. microalgae were found to be suitable for growth in this pre-treated reject water. Typical nitrogen removal was 80-90 g N/kg TSS of produced microalgae. The microalgae were successfully harvested by chemically assisted flocculation followed by straining through a 33 μm sieve cloth, achieving up to 99% recovery. Harvested algae were anaerobically co-digested with wastewater sludge. The specific methane gas production (mL CH 4/g VS fed) for the algae varied from less than 65% to 90% of the specific methane gas production for the wastewater sludge, depending on digester temperature, retention time and pre-treatment of the algae biomass. © IWA Publishing 2011.

Sahu A.K.,Aquateam Norwegian Water Technology Center | Sahu A.K.,University of Stavanger | Siljudalen J.,Biowater Technology | Trydal T.,University of Stavanger | Rusten B.,Aquateam Norwegian Water Technology Center
Journal of Environmental Management | Year: 2013

The feasibility of growing microalgae in natural light using wastewater high in nutrients (N & P) for the production of more bioenergy was examined. The main retrofitting unit would be a photobioreactor for wastewater treatment plants (wwtp) having anaerobic digesters in close proximity. Theoretical microalgae production rates from different wastewater sources (municipal wwtp, source separation of human and animal wastewaters) were estimated using mass balance. Mass and energy balances for a conventional wwtp using chemically enhanced primary treatment was investigated for microalgae growth for a situation limited by availability of carbon dioxide (CO2) generated onsite and where additional CO2 was imported from outside source. Reject water from dewatering of anaerobically digested sludge from four wwtp around Oslo region were pretreated for improved light penetration and examined for microalgae growth. Several pre-treatment methods were investigated. Pretreatment using flocculation+settling+anthracite filtration yielded high light transmittance. A maximum microalgae growth rate of 13g TSS/m2-d was achieved using this pretreated reject water. The challenges of integrating photobioreactors with existing units have been highlighted. © 2013 Elsevier Ltd.

Wang M.,University of Massachusetts Amherst | Sahu A.K.,Aquateam Norwegian Water Technology Center | Rusten B.,Aquateam Norwegian Water Technology Center | Park C.,University of Massachusetts Amherst
Bioresource Technology | Year: 2013

The study investigated the growth characteristics of environmental algal strain, Chlorella, in the modified Zarrouk medium and its anaerobic co-digestion with waste activated sludge (WAS). Analysis of extracellular polymeric substances (EPS) in algal culture and WAS indicated that Chlorella secreted more EPS into the surrounding liquid than formed floc-associated EPS as in activated sludge. Mesophilic anaerobic digestion of algae alone required extended digestion period to produce methane, with biogas yield at 262mL/gVSfed after 45days of digestion. When algae was co-digested with varying amounts of WAS, 59-96% in mass, not only biogas yield of microalgae improved but the gas phase was reached more quickly. The dewaterability of co-digestion products were also better than two controls digesting WAS or algae only. These results suggest that anaerobic co-digestion of algae and sludge improves the digestibility of microalgae and could also bring synergistic effects on the dewaterability of digested products for existing anaerobic digesters. © 2013 Elsevier Ltd.

Paulsrud B.,Aquateam Norwegian Water Technology Center | Rusten B.,Aquateam Norwegian Water Technology Center | Aas B.,The Filter
Water Science and Technology | Year: 2014

The objective of this study was to compare some basic characteristics of sludge from fine mesh sieves (sieve sludge) with sludge from primary clarifiers (primary sludge) regarding their energy potential with a focus on anaerobic digestion and/or incineration. Nineteen samples of sludge from fine mesh sieve plants (most of them without fine screens and grit chambers as pre-treatment) and 10 samples of primary sludge were analysed for the content of dry solids (DS), volatile solids (VS), chemical oxygen demand (COD), calorific value and methane potential. The results demonstrated that the sieve sludges have significantly higher VS content and higher methane potential than primary sludges, clearly indicating an increased sludge energy potential if fine mesh sieves are used for primary treatment instead of primary clarifiers at wastewater treatment plants with anaerobic digesters. If the sludges from primary treatment are to be incinerated or used as fuel in cement kilns, there is no significant difference in energy potential (given as calorific values) for the two types of primary treatment. © IWA Publishing 2014.

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