Short-Term Effects of Low pH on the Microfauna of an Activated Sludge Wastewater Treatment System

Abstract

Optimum pH for biological (e.g., activated sludge) wastewater treatment is stated to lie between pH 6.5 and 8.0; however, the pH of processed effluent from thermomechanical pulp mills is closer to 4.5 and 5.5. Consequently, pH adjustment of effluent is required with associated costs. The ability of the microfaunal community (protozoa and metazoa) of activated sludge to survive at pH levels below 6.5 was evaluated with samples collected from Corner Brook Pulp and Paper Ltd. (Newfoundland, Canada). Effect of pH was examined at “high pH” (4.5, 5.5 and 6.5 control) and “low pH” (2.5, 3.5 and 6.5 control) under “summer” temperatures of 30°C and “winter” temperatures of 15°C, with impacts assessed after 1 h and 24 h exposure. Effect of pH was found to be temperature-dependent: pH levels down to 4.5 appeared to have little impact on microfaunal abundances at 30°C , but a number of microfauna were negatively affected at 15°C. Low pH levels of 2.5 and 3.5 were detrimental to the population densities of most microfauna. Adverse pH effects were more marked with increased exposure in some cases. An acid-neutralizing ability may be inherent in the activated sludge, as treatment pH increased over 24 h.

Impact of hazardous events on the removal of nutrients and trace organic contaminants by an anoxic–aerobic membrane bioreactor receiving real wastewater

“…The mixed liquor pH increased from 7.1 to 8.3 and 7.2 to 8.4 for the anoxic and the aerobic bioreactors, respectively following ammonia shock. In agreement with Trinh (2013), the pH levels returned to the normal operation range within 72 h. Such temporary pH variation may not significantly affect bulk organics removal since the optimum pH for biological process is thought to lie between pH 6.5 and 8.0 (Baldwin and Campbell, 2001). However, this may have significant impact on the removal of some specific TrOCs as further discussed in Section 3.3.…”

Efficiency Limiting Factors of Petrochemical Wastewater Treatment Using Hybrid Biological Reactor

“…The pH during all experiments varied in the range of 6.9 to 7.9 while increasing continuously during each experiment. This range of pH is conformant to the optimum conditions for biological wastewater treatment, according to Baldwin and Campbell (2001). The observed increase in pH indicated no accumulation of acidic intermediates formed during the biodegradation (Chavan & Mukherji, 2010).…”

Performance of Membrane Biological Reactor for Tobacco Industrial Wastewater Treatment

“…Meanwhile, as the mixed liquor pH decreased to 5.5 and below, the microbial activity has worsen revealing low %COD removal. Thus, low pH can interfere with the degradation mechanism of some bacterial species [21] [22] including Bacillus and Pseudomonas. Additionally, Bhattacharyya et al [23] reported that heterotrophic bacteria favor the operation in pH in the range of 7.2 -8.5 [24] [25].…”