Wastewater Treatment Plant Upgrade
The City of Moose Jaw’s Wastewater Treatment Plant (WWTP) is the first plant in Western Canada to use the Biolac Wave Oxidation™ process for Biological Nutrient Removal (BNR). The Biolac Wave Oxidation™ process is a suspended growth activated sludge process primarily aimed at BOD and Nitrogen reduction from wastewater. The Biolac Wave Oxidation™ process uses a simple control of the air flow distribution to the Biolac’s moving aeration chains, varies the basin dissolved oxygen content by creating a unique moving wave of multiple oxic and anoxic zones. This repeated cycling of environments nitrifies and denitrifies the wastewater in one basin without the need of recycle pumping or additional external basins. The system at this WWTP consists of earthen basin bioreactors with submerged aeration supporting a suspended growth activated sludge process and final clarifiers to separate biological solids from the liquid stream.
Upgrades to the WWTP expanded the treatment capacity to 24,000 m3/d thereby accommodating increased industrial and municipal wastewater contributions while maintaining treated effluent irrigation agreements with the neighboring Baildon Region. Construction on this $26 million upgrade commenced in October 2007 and has been in operation since early 2010. The plant was designed to achieve a monthly average TSS of 15 mg/L, BOD of 15 mg/L, TN of 10 mg/L and NH3_N of 1 mg/L. The plant uses alum for phosphorus reduction to below 1 mg/L. The effluent is UV disinfected before it is released to the Moose Jaw River.
The City of Moose Jaw has upgraded its wastewater treatment system to include an extended aeration Biolac Wave OxidationTM process resulting in the reduction of ammonia nitrogen levels to desired limits. Additionally, a UV disinfection system was installed to replace the use of chlorine thereby eliminating the concern for aquatic environment in the Moose Jaw River. The plant was commissioned in early 2010 and has been in operation ever since then. The Biolac Wave OxidationTM process is the first of its kind installed in Western Canada. It is a proven technology in reducing ammonia nitrogen to an acceptable level for discharge into the natural environment. This new treatment process provides a high quality effluent for discharge to Moose Jaw River as well as has storage capability to meet the irrigation demand for the Baildon Region,Moose Jaw.
The City of Moose Jaw had been using an aerated lagoon system to treat its high strength wastewater for over 25 years. The treatment process included alum addition, to coagulate phosphorus, algae and other suspended particles in wastewater, and disinfection with sodium hypochlorite before discharging to the Moose Jaw River. Although the previous treatment system reduced the concentration of major pollutants such as biological oxygen demand (BOD) and total suspended solids (TSS) in the wastewater, it could not sufficiently reduce ammonia concentration. The disinfection of pathogens and concentration of chlorine to the aquatic ecosystem was a major concern from a regulatory perspective. As a result of this concern Environment Canada requested the City of Moose Jaw to develop a Pollution Prevention Plan to control ammonia and chlorine residuals in the treated effluent. In addition, the Saskatchewan Ministry of Environment (MoE) had directed the City of Moose Jaw to provide further treatment to reduce the ammonia concentrations (nitrification) in the wastewater discharges thereby protecting aquatic life in the Moose Jaw River from acute ammonia toxicity.
The City‘s objectives were to have a treatment facility that provides maximum utilization of the existing lagoon and irrigation system and production of a high quality treated effluent that could be discharged to the Moose Jaw River whenever the irrigation demand was low and the storage lagoons were at the full service level (Stantec Consulting Ltd., 2006).
Stantec’s review of MoE requirements and the City’s objectives concluded that discharge of the treated effluent to theMoose JawRivershould be continuous due to: 1) high volumes of treated effluent that would need to be stored during wet weather periods, and 2) potential degradation of the stored effluent in the lagoons.
Expansion of the irrigation system was considered to be an expensive option for the disposal of treated effluent. The existing irrigation system could be used to dispose up to 4,000,000 m3 (80% of the effluent available). However, the irrigation demand fluctuates depending on weather conditions. The irrigation system would need to be expanded to at least four times the size of the existing system to prevent emergency discharge to the Moose Jaw River in the worst wet weather periods.
The process incorporated and optimized existing components of the original treatment system into the WWTP upgrades. Examples include upgrading the existing grit removal system to include coarse bubble air diffusers; and converting treatment lagoon Cells 5 and 6 into sludge storage lagoons. The upgraded plant continues to provide storage for treated water for irrigation to the Baildon Region.
A new aeration Biolac Wave Oxidation system has been constructed to reduce ammonia nitrogen levels to desired limits. During winter months, clarified effluent (without alum addition) is diverted to storage Cells 4, 7 and 8 for storage while in summer months, the clarified (with alum addition) effluent is UV disinfected and discharged to theMoose JawRiver.
In case of plant maintenance or in an emergency, the new treatment system could be bypassed to Cells 1A, 1 and then 2 to 3.
Figure 1 shows previous treatment system and Figure 2 shows process schematics of the upgraded system at Moose Jaw.
Figure 1 Wastewater Treatment Plant Before Upgrade
Figure 2 WWTP Upgrade Process Schematic
The City’s WWTP faces several treatment challenges given the variable contributions from industrial sources. Although the industrial sector in Moose Jaw accounts for 20% of the water use, the variable operation of the meat and pork packing plants causes adverse fluctuations in wastewater strength. These conditions include higher levels of organic carbon, nitrogen and phosphorus loads, elevated concentrations of fat, oil, and grease, and occasional odor episodes.
The Biolac Wave Oxidation™ System installed at Moose Jaw WWTP is a proprietary process that combines long solids retention times with alternating multiple stages of aerobic and anoxic conditions. This process allows for biological nitrification and denitrification to occur in time changes rather than in space by using timers to cycle the air flow to bundles of aeration assemblies. The process is a low cost alternative and is simple in operation. The Biolac system utilizes a longer sludge age (30-70 days) than other conventional aerobic systems (15-25 days). This long sludge age dramatically reduces effluent BOD and ammonia levels. The Biolac’s moving aeration assemblies varies the basin dissolved oxygen content by creating a unique moving wave of multiple oxic and anoxic zones where nitrification and denitrification occurs. Fine bubble diffuser assemblies, BioFusers, are suspended above the basin floor by the BioFlexTM moving aeration chains. The motion of the chains and diffusers distribute the oxygen transfer and mixing energy evenly throughout the basin. Figure 3 shows BioFlex BioFuser assemblies.
Figure 3 BioFlex and BioFuser Assemblies
Alum is added to the effluent after exiting the Bioreactor basin but before the clarifier. The flocculated sludge settles to the bottom of the clarifier and supernatant is directed to the UV component where it is disinfected and discharged to the Moose Jaw River. In an emergency shutdown mode the supernatant is directed to the storage lagoon.
Treated Water Quality
The anticipated effluent discharge criteria to be implemented by the City of Moose Jaw by 2010 was TSS < 30 mg/L, BOD < 30 mg/L, TP < 1 mg/L, NH3_N < 7.1 mg/L and Fecal Coliform counts < 100/100 mL monthly average. The E. coli count limit was recently revised by MoE from 200 mpn/100 mL geometric mean monthly, “to” not to exceed 200 mpn/100 mL. The plant was designed to meet monthly average TSS of 15 mg/L, BOD5 of 15 mg/L, TN of 10 mg/L, NH3_N of 1 mg/L, TP of 1 mg/L and Fecal coliform count of 100/100 mL in the treated effluent.
Figure 4 shows influent BOD and TSS concentrations in wastewater at Moose Jaw.
Figure 4 Influent BOD and TSS Concentrations
The average influent BOD and TSS concentrations at Moose Jaw wastewater treatment are 178 mg/L and 233 mg/L, respectively. The treated effluent BOD and TSS concentrations are 6.1 mg/L and 7 mg/L, respectively which are well below the design target of 15 mg/L and discharge criteria of 30 mg/L each for BOD and TSS. Figure 5 shows effluent BOD and TSS concentrations at the Moose Jaw Waste Water Treatment Plant.
Figure 5 Effluent BOD and TSS Concentrations
The raw wastewater at the Moose Jaw Waste Water Treatment Plant contains an average of 31.4 mg/L of Kjeldahl nitrogen and 18 mg/L of Ammonia nitrogen. The ammonia nitrogen and nitrate nitrogen in the effluent are 0.2 mg/L and 16.2 mg/L, respectively. Figure 6 shows influent and effluent nitrogen concentrations in various forms. As noted in Figure 6, the nitrogen in the effluent is in the form of nitrate due to excess air supply in the bioreactors due to aeration mixing requirement.
Figure 6 Influent and Effluent Nitrogen Concentrations
The raw wastewater at Moose Jaw Wastewater Treatment Plant contains average phosphorus of 4.3 mg/L. The average phosphorus concentration in the effluent is 0.6 mg/L which is well below the anticipated value of 1 mg/L. Figure 7 shows influent and effluent phosphorus concentrations at Moose Jaw Waste Water Treatment Plant.
Figure 7 Influent and Effluent Phosphorus Concentrations
The wastewater at the MJWWTP is UV disinfected before releasing to the Moose Jaw River. An average concentration of E. coli in the effluent was anticipated to be 100 MPN/100 mL and the plant is meeting this requirement most of the time. Figure 8 shows E. coli concentrations in the effluent.
Figure 8 E. coli Concentrations in the Effluent
The Moose Jaw Waste Water Treatment Plant exceeds all discharge criteria anticipated. The Biolac system, which was fist of a kind installed in the Western Canada for nitrogen reduction, has proven to be an efficient and effective system in cold climate. The ammonia nitrogen concentrations are well below the discharge limit; the BOD and TSS levels in the effluent are consistently below the design targets.