Enhanced biological phosphorus removal (EBPR) relies on diverse but specialized microbial communities to mediate the cycling and ultimate removal of phosphorus from municipal wastewaters. However, little is known about microbial activity and dynamics in relation to process fluctuations in EBPR ecosystems. Here, we monitored temporal changes in microbial community structure and potential activity across each bioreactor zone in a pilot-scale EBPR treatment plant by examining the ratio of small subunit ribosomal RNA (SSU rRNA) to SSU rRNA gene (rDNA) over a 120 day study period. Although the majority of operational taxonomic units (OTUs) in the EBPR ecosystem were rare, many maintained high potential activities based on SSU rRNA : rDNA ratios, suggesting that rare OTUs contribute substantially to protein synthesis potential in EBPR ecosystems. Few significant differences in OTU abundance and activity were observed between bioreactor redox zones, although differences in temporal activity were observed among phylogenetically cohesive OTUs. Moreover, observed temporal activity patterns could not be explained by measured process parameters, suggesting that other ecological drivers, such as grazing or viral lysis, modulated community interactions. Taken together, these results point towards complex interactions selected for within the EBPR ecosystem and highlight a previously unrecognized functional potential among low abundance microorganisms in engineered ecosystems.

In this investigation, a laboratory-scale enhanced biological phosphorus removal (EBPR) process was operated under controlled conditions to study the impact of varying the influent ratio of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TP), and the consequential biochemical reactions on oxygen transfer parameters. The data showed that the experiment with high influent phosphorus relative to nitrogen (COD/TP = 51 and TKN/TP = 3.1) achieved higher alpha and oxygen transfer efficiency (OTE(f)). On the other hand, the experiment with high influent nitrogen relative to phosphorus (TKN/TP = 14.7 and COD/TP = 129) resulted in approximately 50% reduction in alpha and OTE(f) under similar organic loading. This suggested that the intracellular carbon storage and the enhanced biological P removal phenomenon associated with the phosphorus-accumulating organisms (PAOs) had a positive influence on OTE(f) in the high phosphorus experiment compared to an active population of nitrifying and denitrifying organisms in the high nitrogen experiment. The intracellular carbon storage by the glycogen-accumulating organisms also appeared to have had a positive effect on oxygen transfer efficiency, although to a lesser extent in comparison to the PAOs. It was also found that oxygen uptake rate (OUR) was not a good indicator of the measured alpha and OTE(f), because it was a combined effect of several biochemical reactions, each having a varying degree of influence. It is difficult to underestimate the crucial role of flocs in mass transfer of oxygen, because microorganisms associated with flocs carry out the biochemical reactions. It seems that the combination of influent characteristics and biochemical reactions in each experiment produced a unique biomass quality (determined by the biomass N to P ratio), ultimately affecting the mass transfer of oxygen. A theoretical explanation for the observed oxygen transfer efficiency under the process conditions is also proposed in this article.

In this investigation, the mass transfer of oxygen was determined using four different testing methods in three activated sludge processes, as per the guidelines established by the American Society of Civil Engineers (ASCE 1997). The testing methods applied included the steady-state oxygen uptake rate (OUR), the non-steady-state changing power level (CPL), the non-steady-state hydrogen peroxide addition (HPA) and the off-gas methods. The analysis indicated that steady-state OUR and off-gas methods resulted in comparable estimates of oxygen transfer parameters, with somewhat higher variations observed in the data from the off-gas method. The application of HPA and CPL methods produced variable results under the same process conditions and these testing methods affected the process. Based on the comparative evaluation conducted in these controlled experiments, the validity of HPA and CPL tests to measure the oxygen transfer under process conditions is questionable. Overall, the off-gas method appears to be superior, as it does not require steady-state process conditions. However, under suitable conditions the steady-state OUR method may be an economical option to study oxygen transfer under process conditions.

In this study, the mass transfer coefficient of biological floc (K(L)a(bf)) was estimated from the mass transfer coefficient of the mixed-liquor (K(L)a(f)) and the reactor-solution (K(L)a(e)). The biological floc resistance (BFR) and reactor-solution resistance (SR) were defined as the reciprocal of K(L)a(bf) and K(L)a(e), respectively, by applying the concept of serial-resistance originally presented in two-film theory (Lewis and Whitman (1924) Ind Eng Chem 16:1215-1220). The specific biological floc resistance (SBFR) was defined as biological floc resistance per unit biomass concentration. The data indicated that an activated sludge process yielding low BFR/MLR and BFR/SR tended to produce higher oxygen transfer efficiency. Surprisingly, the reactor-solution posed the same level of resistance as clean water in all experiments, except in a 5-day SRT, non-nitrifying, completely mixed activated sludge (CMAS) process run. Furthermore, SBFR successfully represented biological floc and showed a positive correlation to sludge volume index (SVI). In addition, SBFR/SR and oxygen transfer efficiency (OTE(f)) followed an exponential relationship for the complete data set. The method of separating the mixed-liquor into biological floc and reactor-solution improved the understanding of oxygen transfer under process conditions, without resorting to intrusive techniques or direct handling of fragile biological floc.

A laboratory scale enhanced biological phosphorus removal process was operated in the University of Cape Town configuration to study the variations in alpha and oxygen transfer efficiency (OTEf) under different process conditions. As part of this investigation, process oxygen transfer parameters were determined using the steady state oxygen uptake rate (OUR) and the nonsteady state hydrogen peroxide addition (HPA) methods, as per the American Society of Civil Engineers guidelines. The results indicated that the oxygen transfer parameters [volumetric mass transfer coefficient (K(L)a(f)), oxygen transfer rate (OTRf), alpha and OTEf)] were higher when both methods were applied on the same day, compared to the subsequent period, when only the steady state OUR method was employed, under similar operating conditions. The difference in the oxygen transfer parameters appears to be due to the addition of H2O2 that generates reactive oxygen species in the nonsteady state HPA test. Based on the findings, it was concluded that the HPA test was not a suitable technique to measure oxygen transfer under process conditions. Further, a conceptual model hypothesizing the impacts of H2O2 addition on activated sludge process is presented.

Biological nutrient removal (BNR) technology for wastewater treatment was originally imported from South Africa in the early 1980s to protect the water quality of Okanagan Lake in central British Columbia from the effects of eutrophication. Since that time, more than 10 BNR plants have been built in western Canada, with capacities ranging from 2000 to 500 000 m3/d. As a result of the interaction among university researchers, plant designers, and plant operators, considerable progress has been made in refining the understanding of process and adapting the technology for cold climates. Consulting engineers from western Canada are now successfully competing in the international marketplace in the application of BNR technology in the U.S.A., the U.K., Europe, Asia, and Australia.Key words: wastewater treatment, western Canada, biological nutrient removal, nitrogen removal, phosphorus removal, cold climate, technology development.

In this work, pilot-scale, on-line, short-HRT fixed-film prefermenter systems were evaluated using Ringlace and Kaldnes fixed-film media for short chain volatile fatty acid (SCVFA) production, with screened raw domestic wastewater and primary effluent. In comparison to the control reactors without media, significant levels of SCVFA were generated in the fixed-film prefermenters. For the design considered in this study, the Ringlace media performed well, whereas the Kaldnes media resulted in clogging. The Ringlace media data show that, for a 60-min HRT, on-line prefermenter systems produced 11 and 5.5 mg/L of SCVFA (as acetic acid) with screened raw wastewater and primary effluent, respectively. Such a low HRT might translate into potential cost savings (up to 25%) in providing SCVFA to enhanced biological phosphorus removal (EBPR) plants and could lead to a completely new generation of prefermenter designs.Key words: domestic sewage, enhanced biological phosphorus removal systems, fixed film, prefermenter, short chain volatile fatty acids.