This paper reports on a possible technique to determine specific nitrification and denitrification rates (SNR and SDNR) in an oxidation-reduction potential (ORP) controlled, intermittent aeration (IA) tank, in which simultaneous nitrification and denitrification (SND) occurred. In addition, SNRs in a three-stage Bardenpho aerobic zone and SDNRs in its anoxic zone were determined. This research was done at bench scale. The technique involves a steady-state run and two additional transient-state tests (created by either ammonia or nitrate shock loading). The rates obtained, using this technique, are the maximum rates possible in a continuous process under certain, improvised conditions. The technique is extremely flexible and generates data relating the rate to substrate concentration in one steady-state run. Data analysis was performed using the integral method; an excellent agreement between predicted and experimental data was found. Zero-order kinetics could describe nitrification in an ammonia concentration range of 1–30 mg/L and denitrification in a nitrate concentration range of 10–30 mg/L. The SNRs in the intermittently aerated, complete-mix (IACM) tank (0.39–1.69 mg g–1 h–1) were considerably lower than those in the 3-stage Bardenpho aerobic zone (3.4–3.81 mg g–1 h–1) due mainly to imposed dissolved oxygen limitations. The SDNRs in the IACM tank were in a range of 0.16–1.26 mg g–1 h–1, which were also considerably lower than that in the 3-stage Bardenpho anoxic zone (2.0–2.5 mg g–1 h–1). Key words: acetate, denitrification, intermittent aeration, kinetics, methanol, nitrification, ORP control, simultaneous nitrification and denitrification.

Pilot testing of a fluidized bed reactor used to recover phosphate, in the form of struvite, from anaerobic digester supernatant was conducted at the Advanced Wastewater Treatment Plant, City of Penticton, British Columbia. The main objective of this study was to demonstrate the ability of the reactor to remove at least 70% of the phosphate in the supernatant from a digester fed with a combination of primary and secondary sludge. It was found that the operation of the reactor could be controlled to achieve any desired level of phosphorus removal up to 90%. Analysis of the recovered struvite crystals showed essentially pure struvite (>99% by weight) with small amounts of calcium (<0.5% by weight) and traces of potassium and iron. The recovered crystals had mean diameters increasing from 0.5 to 1.8 mm over the course of the study. The increasing diameters are believed to be the result of changes in the crystal structures that caused them to become stronger over the course of the study.Key words: crystallization, nutrient removal, phosphorus recovery, struvite, sludge treatment, wastewater.

The primary goal of this research was to determine the effect of methanol-induced denitrification on volatile suspended solids production, settleability, and oxidation-reduction potential in a full-scale sequencing batch reactor. Batch tests were also conducted to determine the influence of mixing and acclimatization on the denitrification of wastewater with methanol. The observed sludge production in the full-scale sequencing batch reactor with methanol addition was 0.21 kg volatile suspended solids V methanol, versus the calculated stoichiometric sludge production of 0.17 kg volatile suspended solids l(-1) methanol. The settleability in the full-scale sequencing batch reactor, measured by the sludge volume index, increases linearly with increasing denitrification rate. The total change in the oxidation-reduction potential magnitude during a sequencing batch reactor cycle increased linearly with increasing denitrification rate. A minimum of 55% increase in the denitrification rate was observed in a batch reactor with methanol addition and a sludge acclimatized to methanol addition, compared to a batch reactor with methanol addition and a non-acclimatized sludge. The non-acclimatized batch reactor had a negligible denitrification rate without methanol addition. However, significant denitrification rates were observed in the acclimatized batch reactors without methanol addition, potentially caused by n-dcrobial storage or an increased population of denitrifiers that scavenge any available carbon. A completely mixed batch reactor, with sludge acclimatized to methanol addition during the anoxic cycle, had an increase in the denitrification rate ranging from 660%, without methanol addition, to 200%, with a methanol dosage of 12.7 mg l(-1), compared to the unn-dxed batch reactor with an acclimatized sludge. Therefore, mixmg appears to be critical to the denitnfication process, to realize the best kinetic performance.

The primary goal of this research was to determine the potential for denitrification and phosphorus removal of a full-scale sequencing batch reactor (SBR), with and without the use of methanol as an external carbon source. The control SBR, without methanol addition, achieved negligible denitrification. Two denitrification rates were observed in the experimental SBR, with methanol addition; an initial fast rate and a slower second rate. The denitrification rate during the first rate period increased with increasing methanol concentration, until a maximum denitrification rate of ∼19 mg NOx-N/g MLVSS/day was attained. Following the depletion of the methanol, denitrification reactions probably continued by using the available natural carbon in the influent, resulting in a slower, second denitrification rate. Biological phosphorus uptake and release was significant only in the SBR with methanol addition. Methanol was probably not utilized as the carbon source for the enhanced biological phosphorus removal (EBPR) process. However, methanol addition was critical, since it depleted the available nitrates and thus allowed EBPR to take place.

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.

Methanol was applied to a full-scale continuous inflow SBR, as a carbon source for denitrification and possible phosphorus removal. This research was conducted at the District of Kent Wastewater Treatment Plant in Agassiz, British Columbia, Canada. This plant employs two SBR's working in parallel; one unit was used as a control, without the addition of methanol. There was no difference in the overall total nitrogen removal efficiency through methanol addition; however, the additional carbon source significantly shortened the denitrification reaction time in the existing reactor. The high nitrogen removal efficiency, with or without methanol addition, was primarily due to the advantages provided by continuous-flow SBR carbon loading. The phosphorus removal efficiency in the experimental SBR was also consistently higher than in the control SBR. The solids production from methanol addition was estimated to vary between 0.18 and 0.29 gVSS/gCH(3)OH. Methanol addition also had an influence on the settling qualities of the sludge.

This bench-scale research investigated the controlling factors for simultaneous nitrification and denitrification (SND) in a 2-stage, intermittent aeration (IA) process, designed for nitrogen and phosphorus removal. The 2-stage process consisted of an anaerobic zone followed by an oxidation–reduction potential (ORP) controlled, intermittently aerated, completely mixed (IACM), tank. The three independent variables examined were the average ORP level, organic substrate (acetate and methanol) dosage and aeration cycle. The sewage used was completely of residential origin. Nitrogen balance clearly indicated that the nitrogen loss, due to SND in the aeration tank, contributed 10% to 50% of the influent TKN to the overall nitrogen removal. Significant differences in both nitrification and denitrification in the IACM tank were observed, when different average ORP levels were applied to the aeration control; this proved that absolute ORP can be used as a real-time control parameter for SND. Under low DO and intermittent aeration conditions, acetate and methanol additions improved nitrification over the entire dosage range and denitrification at relatively low dosages. Finally, a longer aeration cycle, with a zero-DO period, appeared to favor sequential nitrification and denitrification (SQND), not SND.

A bench-scale, continuous-flow, study was conducted to investigate the factors affecting phosphorus removal in a two-stage, intermittent aeration (IA) process. The two-stage process used consisted of an anaerobic zone and an intermittently aerated, completely mixed (IACM) tank, in which intermittent aeration was controlled by absolute ORP. The factors examined were the average ORP control level (used for aeration control), external acetate dosage, and intermittent aeration cycle. The degree of phosphorus removal in the two-stage IA process depended mainly on the presence of acetate in the anaerobic zone. The average ORP control level also affected the phosphorus removal at relatively low external acetate dosages. Small phosphorus release in the presence of nitrate and dissolved oxygen was observed during the air-off period. This suggests that a relatively long aeration cycle should be avoided in the two-stage IA process for preventing significant phosphorus release in the IACM tank.

The enhanced biological phosphorus removal (EBPR) activated sludge process is a wastewater treatment process by which not only organic pollutants but also phosphorus are removed. In the EBPR process, it is known that organic matter in the influent is removed in the anaerobic phase of the sequencing anaerobic and aerobic conditions. Although the mechanism of the anaerobic substrate uptake is being revealed, the existing observations are based on the experiments with activated sludge acclimatized with synthetic sewage, or synthetic media. In this study, the anaerobic substrate uptake by EBPR activated sludge treating real sewage was examined. The sludge was obtained from a pilot plant of the University of British Columbia, Canada. And as the substrate, acetate, propionate, lactate, pyruvate, malate, succinate, and fermented sewage were examined. The results clearly showed that most part of the sink of carbon anaerobically taken up is explained by PHA (poly 3-hydroxyalkanoates), and that glycolysis is playing a significant role in the anaerobic uptake of acetate and propionate.

This study explored the effect of pH on the acid-phase anaerobic digestion of primary sludge. Controlled and uncontrolled pH experiments were conducted using two bench-scale, continuous-flow reactors having different configurations: a completely mixed reactor (CMR) with clarifier and solids recycling, and an upflow anaerobic sludge blanket (UASB) unit. Results indicate that the specific rates of VFA production and COD solubilization, in either system, were not affected by the variation in pH between 4.3 and 5.2, but at higher pH values (5.9-6.2) a significant decline (by 25-30%) in both parameters was observed. Analysis of the degradation behavior of the three important organic classes (carbohydrates. proteins, and lipids) revealed that each class followed an individual trend with respect to pH changes. Acetic acid was the major end-product of acidogenic digestion in both reactors, regardless of pH. The percent VFA distribution did not appear to be influenced by pH variation, except for propionic and butyric acids. Besides VFAs, small amounts of formic acid, ethanol, and lactic acid were also formed at all pH values tested.

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate.

This study investigated the effect of certain operational and environmental parameters [hydraulic retention time (HRT), solids retention time (SRT), pH, and reactor configuration] on substrate degradation during the acid-phase digestion of municipal primary sludge. Experiments were conducted using two bench-scale, continuous-flow bioreactors, having different configurations: a completely mixed reactor (CMR) with clarifier and sludge recycling; and an upflow anaerobic sludge blanket (UASB) unit. Results indicate that the utilization percentages of the three major constituents of primary sludge (carbohydrates, proteins, and lipids) are significantly affected by variations in HRT and pH. Changes in SRT however influence only protein dissimilation, at least in the range investigated. Moreover, carbohydrate and lipid degradation patterns are dependent on reactor configuration, whereas protein utilization appears to be independent of the reactor regime.

A series of bench-scale, continuous-flow experiments, using primary sludge from a local municipal wastewater-treatment plant, has been employed to investigate the effect of hydraulic retention time (HRT) on the acid-phase anaerobic digestion process. Results show that both volatile fatty acid (VFA) production and chemical oxygen demand (COD) solubilization increase significantly with increasing HRT up to 12 h, but drop moderately at a longer HRT. Acetic acid and propionic acid are the main VFAs formed, averaging 46% and 32% of the total, respectively. Variation in HRT has a profound effect on organic substrate degradation as well. Regardless of the prevailing experimental conditions, lipids and carbohydrates are converted at higher percentages than proteins. Furthermore, protein utilization appears to be independent of reactor configuration, but carbohydrate and lipid degradation patterns are a function of the reactor regime.

Abstract The effects of certain operational and environmental parameters on the acid-phase anaerobic digestion of primary sludge have been investigated using a series of bench-scale, continuous-flow experiments. Short-chain volatile fatty acids (VFA), the main products of the process, are preferred substrates for the bacteria involved in the biological removal of phosphorus. Results show that the net volatile fatty acid generation improves with an increase in hydraulic retention time (up to 12 hours) as well as in solids retention time. Although acid production is not affected by a decrease in pH from 5.1 to 4.5, the production is significantly lower (25 to 30%) at pH of about 6.0. The use of different feed sources influences to some extent the amount of product formation. Moreover, lipid and carbohydrate degradation patterns are dependent on reactor configuration, whereas protein utilization appears to be independent of the reactor regime. The amount of VFA produced, in most cases, is high enough to support biological phosphorus removal processes.

A series of laboratory-scale, continuous flow experiments has been employed to study the effects of selected HRTs and SRTs on the acid-phase fermentation of primary sludge. The VFA production is greatly affected by the variation in both operational parameters. Overall, HRTs from 9 to 15 hours and SRTs from 10 to 20 days result in high rates of substrate solubilization and subsequent VFA generation.

A brief review of recent developments in biological nitrogen and phosphorus removal technology is presented. Guidelines are outlined of how current understanding of these two removal mechanisms can be applied in the upgrading of existing wastewater treatment plants for biological nutrient removal. A case history dealing with the upgrading of the conventional activated sludge process located at Penticton, British Columbia, to a biological nutrient removal facility with a design flow of 18,200 m3/day (4.0 IMGD) is presented as a design example. Process components requiring major modification were the headworks, bioreactors and sludge handling facilities.

The objective of this research was to test the feasibility of using nitrate as sole electron acceptor for biological phosphate removal from wastewater. Two sequencing batch reactors, one with nitrate and the other one with air to supply oxygen, were used to develop two sets of acclimated biomass. It was shown that it was possible to induce biological phosphate removal with nitrate alone, confirming the ability of denitrifying bacteria for this process. A preliminary comparison, however, suggested that nitrate may be less efficient than oxygen for phosphate uptake.