In spite of budget constraints, the Water and Wastewater Optimization Section of the Ministry of Environment and Energy (MOEE) and the Great Lakes 2000 Clean Up Fund (GL2000CUF) of Environment Canada have been active in leading the development and application of innovative treatment technologies and optimization approaches for the municipal water and wastewater treatment indus-tries. Four projects related to optimizing sewage treatment plants (STPs) for nitrification requirement are presented in this issue.

Increasingly, more sewage treatment plants are being required to achieve nitrification when undergoing plant expansion. The requirement is necessary to eliminate effluent toxicity to aquatic life, and in some cases to reduce oxygen demand in the receiving water. Nitrification requires more process air than for carbonaceous BOD (CBOD) removal; the resulting sludge is also more difficult to settle. Consequently, STPs with nitrification requirements are often designed with larger aeration tanks and final clarifiers.

MOEE and GL2000CUF commissioned a literature review in 1993 to identify innovative approaches to improve aeration and clarification systems to bring down their capital and O&M costs.

The literature review concluded that by applying innovative technologies, hundreds of millions of dollars can be saved by Ontario STPs when they are being expanded/upgraded to comply with nitrification requirement. Currently, three field demonstration projects are being carried out at Tillsonburg, Waterdown and Woodward Avenue STPs to test some of the innovative technologies identified by the literature review.

The Tillsonburg STP project is carried out by the Wastewater Technology Centre (WTC). It evaluates the cost benefits, and the optimum design and operating conditions of on-/off- aeration control. This control strategy provides an alternating sequence of aerobic and anoxic conditions within the same aeration tank.

Anoxic conditions provide several advantages: reduction in subsequent aeration and energy requirement, recovery of alkalinity loss during the nitrification process and better settling sludge. The mechanical retrofits may be as simple as installing timers to allow cycling of surface aerators, or to open and close electrically actuated valves on the diffused air supply. Once the aeration cycle times are set, only seasonal adjustments may be required to allow for changes in sewage temperature. Baffling of aeration tanks and mixed liquor recycle are not necessary with this operating strategy.

Tillsonburg STP is a 8,200 m3/day, conventional activated sludge plant, serving a population of 11,000. Aeration and mixing are provided by coarse bubble diffusers and a combination of fixed and variable speed blowers. The plant is also equipped with an on-line computer control system to maintain a pre-set dissolved oxygen concentration in the aeration tanks.

For this study, the plant is divided into two equal parallel trains: the studied (S) train and the control (C) train. Retrofit comprises incorporating two software programs into the on-line computer system to manipulate blower speed and aeration on-/off- times.

Field testing commenced in July, 1995. The on-/off- cycle in the S train was kept at 30 minutes each, with 2 short bursts of aeration during the off- cycle to maintain mixing in the aeration tanks. Results to-date showed that at 18o C and 5 days SRT, average effluent total ammonia nitrogen concentration in the S train was higher (1.9 mg/L) than in the C train (0.5 mg/L). These total ammonia concentrations were within the effluent limit of 3 mg/L in summer and 5 mg/L in winter, issued for many Ontario STPs. Average total nitrogen concentration was however, lower in the S train (7.2 mg/L) than in the C train (21.9 mg/L) by 67%. Average and daily CBOD, SS and TP concentrations between the two trains were essentially the same.

The S train also realized an air flow saving of 26% compared to the C train. The study further estimated that a 20% air flow saving is due to oxygen credit obtained during denitrification, and the remaining 6% saving is due to improved oxygen transfer efficiency in the mixed liquor.

The study is on-going to determine efficiency and air flow savings under winter conditions. A similar study is being planned for the Dundas STP which uses mechanical aerators.

Schomberg Water Pollution Control Plant - designed by R.V. Anderson Associates and Rupke & Associates.

The Waterdown STP project is carried out by a consortium of WTC, Totten Sims Hubicki Associates and Enviromega. It evaluates the cost benefits and the optimum design and operating conditions of an integrated fixed film/activated sludge process (IFAS). Results will also be used to assess low cost alternatives for retrofitting the Woodward Avenue STP in Hamilton. The Remedial Action Plan (RAP) has proposed an ultimate effluent limit of 1.0 mg/L TKN for the Woodward Avenue STP.

Nitrifiers tend to grow better in the fixed media and are less prone to wash-out. The fixed media can be added to the existing aeration tanks to increase biomass, and without increasing solids loading to the final clarifiers. Consequently, an IFAS system can be an effective retrofit strategy for many existing STPs.

Two commercial fixed media, Ringlace and Biomatrix, are being tested at the Waterdown STP. Both media are similar in that they are made of plastic ropes and consist of many loops or ringlets per foot of strand. Both media have a very high surface area to volume ratio. The strands are attached to a metal support frame which is installed in the aeration tank to form a non-clogging biomass support media.

The Waterdown STP is a conventional activated sludge plant with a design capacity of 2,730 m3/day and a service population of 7,000 people. Both the S and C trains were retrofitted to provide a small anoxic zone. The retrofit was completed in October, 1995. Results to-date showed that ammonia removals were essentially the same in the S and C trains during warm weather and at lower flows. The S train, however, outperformed the C train during winter and at higher flows. At 12oC, total ammonia concentration was reduced from an average of 15 mg/L in the primary effluent to 5 mg/L in the S train and to 10 mg/L in the C train. It is anticipated that the performance of the S train would further improve once the dissolved oxygen limitation in the S train is corrected. The study is scheduled for completion in early 1997.

The Woodward Avenue STP project is carried out by CH2M Gore & Storrie. It investigates the cost-effectiveness of various baffling strategies to improve final clarifier performance. It is anticipated that more clarifiers will be needed when the Woodward Avenue STP has to comply with the nitrification requirement. In addition, the final clarifiers in the Woodward Avenue STP have had performance problems in the past due to shallow side water depth and mechanical problems with the sludge removal mechanism and leakages at the overflow weir launders. The mechanical and leakage problems were fixed prior to the study.

The study will evaluate three different baffle arrangements: weir baffle alone to redirect wall currents away from the clarifier weirs; weir baffle plus mid-radius baffle; and mid-radius baffle alone to interrupt short-circuiting density currents. Each arrangement will be tested for a minimum of eight weeks, at different hydraulic and solids loading rates. In addition to solids monitoring, dye tests will also be conducted to characterize hydraulic flow patterns.

Evaluation of weir baffle alone is complete. Dye test results showed that the baffle was successful in re-directing the flow from the clarifier side wall towards the interior of the clarifier. However, the S clarifier produced only marginally lower SS concentration (16.4 mg/L) than the C clarifier (19.7 mg/L). The difference is, however, statistically significant at 90% confidence level. The study is scheduled for completion in early 1996.

Ontario has approximately 165 sewage lagoons serving communities of 1,000 people or less. Most of these lagoons discharge in the spring, and their effluent often contains hydrogen sulphide and high ammonia concentration that can be toxic to aquatic life. Furthermore, lagoon effluent often contains high SS due to the discharge of algae and disturbance of bottom sediments.

In 1993, MOEE and GL2000CUF commissioned RV Anderson and XCG to identify alternatives which can be used to improve lagoon effluent quality. Several alternatives including different types of constructed wetland treatment, rock filters, aquaculture, slow rate land treatment, were investigated. The study centered on the "Sutton" concept and ISRSF. The study concluded that the ISRSF used at New Hamburg (started in 1981) and Schomberg (started in 1990), is the most cost-effective alternative.

The ISRSFs are located in the open. The filters in New Hamburg and Schomberg are both 0.8 m in depth and composed of ordinary beach sand. Lagoon effluent in New Hamburg is discharged by spraying intermittently onto the sand filters, and the effluent is collected from the bottom for discharge. In Schomberg, the effluent is applied by flooding the filter surface. Both facilities are in southern Ontario. Filtered effluent is discharged between late March to late November, depending on the weather conditions. In Schomberg, effluent discharge is restricted during July to September.

Long term data at New Hamburg indicated that nitrification is achieved within two to three days of start up in the spring with lagoon effluent temperature remaining at less than 4o C. Between 1991 and 1992, the ISRSF at New Hamburg reduced CBOD from 12 mg/L to 2 mg/L, SS from 17 mg/L to 2 mg/L, TP from 1 mg/L to 0.5 mg/L and total ammonia from 15 mg/L to 0.9 mg/L.

McMaster University was then contracted in 1995 to conduct more detailed site monitoring and laboratory studies to optimize the design parameters for the ISRSF. Both field and laboratory study results concluded that nitrification can start up almost immediately at 4oC or lower, after the sand filter had been freezed for a long period of time. Most of the nitrification occurred at the top 5 cm of the filter, and levelled off at the 20 to 25 cm depth.

The filter loading rate is dependent on the Kg of ammonia to be removed and effluent temperature. The filter size can be further optimized by increasing the discharge rate in the summer, by taking advantage of lower lagoon effluent ammonia concentrations and higher temperature in the summer. More than one filter is necessary as the filter will be clogged after about 20 days of operation. The filter can be returned to service by simply resting it for 10 days. ISRSF effluent TP is dependent on chemical dosage applied to the lagoon content. It is feasible to achieve a TP concentration of 0.3 mg/L with ISRSF.

The study results and experiences have been applied to expand and/or upgrade a number of lagoons in southwestern Ontario, and have resulted in millions of dollars saved. All four projects are co-funded by MOEE, GL2000CUF and the participating municipalities.