Increased Microalgae Growth and Nutrient Removal Using Balanced N:P Ratio in Wastewater

Abstract

Microalgal cultivation using wastewater is now regarded as essential for biodiesel production, as two goals can be achieved simultaneously; that is, nutrient removal efficiency and biomass production. Therefore, this study examined the effects of carbon sources, the N:P ratio, and the hydraulic retention time (HRT) to identify the optimal conditions for nutrient removal efficiency and biomass production. The effluent from a 2nd lagoon was used to cultivate microalgae. Whereas the algal species diversity and lipid content increased with a longer HRT, the algal biomass productivity decreased. Different carbon sources also affected the algal species composition. Diatoms were dominant with an increased pH when bicarbonate was supplied. However, 2% CO(2) gas led to a lower pH and the dominance of filamentous green algae with a much lower biomass productivity. Among the experiments, the highest chlorophyll-a concentration and lipid productivity were obtained with the addition of phosphate up to 0.5 mg/l P, since phosphorus was in short supply compared with nitrogen. The N and P removal efficiencies were also higher with a balanced N:P ratio, based on the addition of phosphate. Thus, optimizing the N:P ratio for the dominant algae could be critical in attaining higher algal growth, lipid productivity, and nutrient removal efficiency.

Utilization of centrate from wastewater treatment for the outdoor production of Nannochloropsis gaditana biomass at pilot-scale

“…This phenomena have found confirmation in the works of Lee et al [39] and Sepúlveda et al [14], who indicated that N removal was higher for P-added media than unbalanced N:P ratio media. To elucidate this aspect the phosphorous balance into the system was performed.…”

Investigation of anaerobic digestion of Chlorella sp. and Micractinium sp. grown in high-nitrogen wastewater and their co-digestion with waste activated sludge

“…However, the N/P ratios after digestion (Table 4) were between 10.3:1 and 15.7:1, which were within the proper range for effective nutrient removal by algae and their biomass growth as suggested by Li et al [35]. The optimal N/P ratio found for Chlorella vulgaris for nutrient removal was 8:1 and the optimal ratio for mixture of microalgae from lagoon was 14:1 [35,36]. The balanced nutrient load, as well as the nearly neutral pH can possibly render the effluents from anaerobic digestion of algae or co-digestion with WAS to become good sources for algae cultivation.…”

Evaluation of Pre-Chlorinated Wastewater Effluent for Microalgal Cultivation and Biodiesel Production

“…However, a significant inverse correlation (p < 0.01) exists between the biomass produced and total nitrogen concentration in the water. Several authors have reported the need for a balanced N:P ratio when using wastewater as the growth medium for microalgae for increased growth and nutrient removal [26,30]. In this study, the total nitrogen concentration far exceeded the total phosphorus concentration at the NWWTW with its optimal N:P of 44.2 exceeding the optimal range of 6.8 to 10 [28].…”

“…Compared to available fossil fuel, biofuels from microalgae is more water intensive [25] with an estimated 3726 kg of water, 0.33 kg of nitrogen, and 0.71 kg of phosphate required for the production of 1 kg of microalgae based biodiesel, if freshwater is used without recycling [26,27], and may be unsustainable for a water stressed country like South Africa. Thus, wastewater presents a solution to this dilemma as it contains nitrogen in the form of nitrates and nitrites, phosphates as well as trace metals necessary for algal growth.…”