Phycoremediation of Municipal Wastewater by the Cold-Adapted Microalga Monoraphidium sp. Dek19.

ABSTRACT Present municipal wastewater treatment technologies often require substantial energy inputs, and fail to completely remove nitrate and phosphate before discharging effluent. In contrast, using the cold-adapted oleaginous microalga Monoraphidium sp. Dek 19 decreased levels of both these polluting ions to 0 mg/dL. Concurrent biomass production was greater at 10 °C than at 22 °C, showing that phycoremediation occurred at low temperatures previously thought to be unsuitable for algal-based treatment. Algal growth with uptake of nitrate and phosphate required only short bursts of aeration to suspend cells and maintain CO2 supply for photosynthesis. To save energy, culture aeration for 1 hour, 4 times per day, including during the dark cycle, yielded cell productivity and phycoremediation nearly equivalent to using 24-hour aeration. The authors conclude that Monoraphidium sp. Dek19 algae represent an economical effluent treatment at cool temperatures found in the high proportion of water resource recovery facilities in geographical areas experiencing cold winters.

Evidence for recycling of inorganic phosphate by wheat chloroplasts during photosynthesis at air levels of CO2 and O2.

Phosphate recycling under photorespiratory conditions was investigated using intact wheat chloroplasts from Triticum aestivum (cv. Maris dove). A decline in the optimal Pi level needed to support steady-state photosynthesis was observed (a) as the bicarbonate supply became limiting, or (b) as oxygen concentrations were increased. Further, at subsaturating CO2 and elevated O2 (52%), photosynthetic induction periods were shortest in the absence of exogenous Pi, and severely extended by its addition. Thus, photosynthesis under low CO2 levels which favor ribulose 1,5 bisphosphate (RuBP) oxygenase activity and glycolate synthesis by chloroplasts decreases their dependency on exogenous Pi from the initial illumination of chloroplasts through to the attainment of steady state rates of O2 evolution. Uptake of phosphate (Pi) was directly measured at ambient O2 concentrations and showed the stoichiometry of O2 evolved to Pi consumed at 10 mmol/L bicarbonate (saturating) had a mean value of 3.0, and was increased to 5.4 at 2.5 mmol/L bicarbonate and to > 8.0 at 1.0 mmol/L bicarbonate. The observation is consistent with enhanced stromal recycling of Pi released during hydrolysis of phosphoglycolate produced in greater quantities as the ratio of RuBP carboxylase relative to oxygenase activities (vc/vo) declines. The theoretical relationship between vc/vo and O2/Pi stoichiometries was derived and compared favorably to experimental data obtained.