Arvo Iital

Evaluation of microalgae production coupled with wastewater treatment

ABSTRACT In the present study, the feasibility of microalgae production coupled with wastewater treatment was assessed. Continuous cultivation of Chlorella sorokiniana with wastewater was tested in lab-scale flat-panel photobioreactors. Nitrogen and phosphorus removals were found to be inversely proportional to the four dilution rates, while chemical oxygen demand removal was found to be 50% at all the tested conditions. The biomass obtained at the highest dilution rate was characterized for its content of lipids, proteins and pigments. The average yields of fatty acid methyl esters (FAMEs), protein, lutein, chlorophylls and β-carotene was 62.4, 388.2, 1.03, 11.82 and 0.44 mg per gram dry biomass, respectively. Economic analysis revealed that potentially more than 70% of revenue was from the production of pigments, that is, chlorophyllin (59.6%), lutein (8.9%) and β-carotene (5.0%) while reduction in discharging costs of the treated wastewaters could account for 19.6% of the revenue. Due to the low market price of biodiesel, the revenue from the above was found to be the least profitable (1.4%). Even when combining all these different revenues, this cultivation strategy was found with the current prices to be uneconomical. Power consumption for artificial light was responsible for the 94.5% of the production costs.

Temporal trends in phosphorus concentrations and losses from agricultural catchments in the Nordic and Baltic countries

This paper in a uniform manner examines temporal trends in phosphorus (P) concentrations and losses from small and well-monitored agricultural catchments in the Nordic and Baltic countries. Thirty-four catchments (range 0.1–33 km2) in Norway (8), Denmark (5), Sweden (8), Finland (4), Estonia (3), Latvia (3) and Lithuania (3) were selected for the study. The time series ranged from 10 (2002–2011) to 21 years (1989–2009). The monthly P concentration and loss time series were tested for significant monotone trends (p < 0.05; two-sided test) using the partial Mann–Kendall test with stream discharge as an explanatory variable. The results show a large variation in concentrations and losses of total phosphorus (TP) among the 34 studied catchments, where the long-term mean annual losses varied from 0.09 to 7.5 kg TP ha−1. In addition, a large interannual variability in losses within catchments was found with up to a factor of 23 between years within the same catchment. Six catchments showed downward temporal trends in the TP loss time series. One upward trend in TP losses was detected in a catchment in south-west Sweden. Eight downward trends were detected in the TP concentration time series. Overall, our results show (1) a huge variability in mean P losses and concentrations among catchments, (2) a huge temporal variability in losses within catchments and (3) few detectable changes in P losses and concentrations over the study period. The results showcase the need for implementation of mitigation strategies towards reduced P losses from agricultural landscapes in the Nordic/Baltic Sea region in order to improve P water quality and ecology in surface waters.

Impact of changes in nutrient inputs to the water quality of the shallow Haapsalu Bay, the Baltic Sea.

This study evaluated the impact of socio-economic and lifestyle changes on nutrient loads and water quality in Haapsalu Bay, the Baltic Sea between 1995-1996 and 2003-2004. Monthly monitoring data of water quality in four rivers discharging to the bay and seawater at five sea stations were used. External input of TN to the bay remained almost unchanged during the study period despite of the somewhat higher riverine load that was explained by intensified agriculture. The TP input decreased by approximately 45% due to the decrease in river and point source loads. Point sources contribute about one-third of the P load to the bay. An overall decreasing gradient from the rivers to the mouth of the bay was observed both for TP and TN concentrations indicating probable removal of these elements from the water column along the east-west transect. In order to keep the TN/TP ratio within the range that suppresses eutrophication in the bay, further efforts must be implemented to reduce point source phosphorus load.