Toxicity of ammonia to algae in sewage oxidation ponds

Abstract

Ammonia, at concentrations over 2.0 mM and at pH values over 8.0, inhibits photosynthesis and growth of Scenedesmus obliquus, a dominant species in high-rate sewage oxidation ponds. Photosynthesis of Chlorella pyrenoidosa, Anacystis nidulans, and Plectonema boryanum is also susceptible to ammonia inhibition. Dark respiration and cell morphology were unaffected by any combination of pH and ammonia concentrations tested, thus limiting the apparent effect to inhibition of the normal function of the chloroplasts. Methylamine had the same effect as ammonia, and its penetration into the cells was found to be pH dependent. Therefore, the dependence of toxicity of amines to algae on pH apparently results from the inability to penetrate the cell membrane in the ionized fonn. When operated at 120-h detention time of raw wastewater, the high-rate oxidation pond maintained a steady state with respect to algal growth and oxygen concentration, and the concentration of ammonia did not excced 1.0 mM. Shifting the pond to 48-h detention time caused an increase in ammonia concentration in the pond water to 2.5 mM, and the pond gradually turned anaerobic. Photosynthesis, which usually elevates the pH of the pond water to 9.0 to 10.0, could not proceed beyond pH 7.9 because of the high concentration of ammonia, and the algal population was washed out and reduced to a concentration that could maintain a doubling time of 48 h without photosynthesis bringing the pH to inhibitory levels. Under these conditions, the pH of the pond becomes a factor that limits the operational efficiency of the oxidation pond.

Ammonia translocation in cyanobacteria

“…Ammonia has also been reported to uncouple cyanobactcrial photosynthesis at high pH [12], since 5 mM ammonia severely inhibited t4CO2 photoassimilation at pH 9 in a number of strains. The degree of inhibition appears, however, to be much reduced in strains that are restricted to growth in alkaline environments, and so may be considered alkalophilic.…”

“…It is perhaps significant in terms of cellular ammonia economy that cyanobacteria are generally very tolerant to high pH, and many can thrive in environments where the pH is 11 or above [11]. Some, but by no means all, become sensitive to raised ammonia concentrations at high pH [12,13]. However, acidophilic strains are almost unknown [14], and one possible explanation is that low external pH would tend to drain the cells of ammonia through diffusion, followed by trappir:g in the protonated form in the outside compartment.…”

Opportunities for phycoremediation approach in tannery effluent: A treatment perspective

“…At full strength (100%) and lower dilution (≥50%), inhibited growth of Spirulina was reported due to the toxic threshold level of ammonia encountered (higher than the 100 mg/L) [91]. The growth of Spirulina evaluated in higher dilution (<40%) of PTE produced higher growth rate than defined medium.…”

“…No effects on cell morphology and dark respiration were observed when below pH 8 and the inhibition effects were noted when the ammonia concentration exceeded 2 mM, at pH ≥ 8.0. Other species investigated for photo and growth inhibition were, Chlorella pyrenoidosa, Anacystis nidulans, and Plectonema boryanum also had the same effect as Scenedesmus obliquus [91]. Effluent dilution or addition of sodium bicarbonate, apparently overcome the ammonia toxicity inhibition in the growth of cyanobacteria cultivated in HRAP system treating tannery effluent [88,89].…”

Effects of Nitrogen Pollution on Periphyton Distribution, Elemental Composition and Assemblage Shifts in River Ecosystems

“…The EPA benthic algae model value for NH 4 þ -N preference is 0.025 mg/L [30]. Other studies have also shown that NH 4 þ -N concentrations >0.028 mg/L inhibit phytoplankton photosynthesis and growth [31]. As levels of NH 4 þ -N increase, epiphyte diatoms in FE may perish, however, filamentous algae have relatively strong tolerances to NH 4 þ -N. We observed that there were no periphyton when NH 4 þ -N concentrations were >2.56 mg/L in the studied rivers, Figure 2.…”