Environmental Science & Engineering - www.esemag.com - January 2003
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Mobile plant improves wastewater treatment at northern work camps

Figure 1: Treatment Plant Schematic.

Work camps have to be established quickly, are of a transient nature and are located in remote and environmentally sensitive areas. Often they are set up during winter, accommodating anywhere between 25 and 400 persons. Utilities such as water and sewerage have to be provided. Wastewater treatment systems located in the north often perform poorly. Given and Smith (1), attributed this to a number of design- and operations-related factors summarized as:

Design-related problems:
- Organic overloading;
- Hydraulic overloading & hydraulic surges; and
- Mixing problems specifically associated with oxidation ditches.
Operations-related problems:
- Failure to scrape hopper-type clarifier walls;
- Failure to maintain sludge returns operative; and
- Underaeration of the mixed liquor.

In response to these deficiencies, and the need to provide for reliable, cost-effective, high-efficiency wastewater treatment, Tanks-a-Lot Ltd. designed a modular, mobile, biologic wastewater treatment plant that is simple, compact, robust, easy to operate and produces a high quality effluent. The treatment objective was only concerned with the reduction of BOD₅ and SS. However, nutrient removal (N and P), could be achieved with minor process modifications and operational adjustments. The process described, is a flexible, biologic, suspended growth system that can be operated in the Conventional Activated Sludge (CAS) or Extended Aeration (EA) mode. The system is designed to treat pre-treated domestic wastewater. Pre-treatment usually consists of a septic tank or at minimum, screens to protect pumps and ancillary equipment from damage. Study Objectives Five major study objectives were established:

Devise a methodology for successful process start-up during winter conditions.
Observe system response under varying hydraulic loading conditions.
Identify operating parameters to achieve a 20/20 effluent.
Observe sludge settleabilty & sludge production.
Identify operator skill level and time requirements.

This article covers a 150 day system performance evaluation and reports only on the operating experience for BOD₅ and SS removal under average hydraulic loadings from 2,300 to 3,500 US gpd (8.7 to 13.2m³/d).

Treatment plant description A schematic of the process component configuration is shown in Figure 1. The pre-treated influent enters the first aeration tank, passes to the second aeration tank and is followed by gravity clarification. The clarifier effluent then flows through two patented Biokinetic™ Units, arranged in parallel. Effluent from the Biokinetic Unit, that serves as a flow-equalization device and mechanical filter, is the process effluent.

The complete wastewater treatment plant is housed in an insulated trailer weighing less than 5,000 kg.

The mobile wastewater treatment plant was located at the Edmonton Capital Region Clover Bar WTP. The influent to the demonstration plant was pumped from the influent of the Clover Bar degritting unit process.

Sampling and analytical protocols For remote work camps usual regulatory effluent compliance parameters are BOD₅ and SS. These were determined from grab samples, recorded and correlated to the operating mode of the module.

The usual operating parameters of MLSS, DO, HRT, SRT, temperature, sludge recycle and sludge settleability were monitored.

Influent characteristics There was a need to establish that the characteristics of the influent wastewater used in this study are similar to those of a pre-treated effluent from a northern work camp. Work camps' wastewater strengths usually average 404 mg/L BOD₅ and 484 mg/L SS (2).

Table 1: Various influent wastewater strengths.

Pre-treatment In many northern work camps, wastewater is pre-treated by a septic tank. By assuming 35 % of the total influent BOD₅ is settleable (3), and 90% of the settleable BOD₅ is removed by settling in the septic tank; that 60 % of the influent SS is settleable (4) and again 90% of the settleable SS is removed, the characteristics of such a pre-treated wastewater will be in the order of 277 mg/L BOD₅ and 223 mg/L SS, respectively.

Some 130 data over the five-month demonstration period for influent BOD₅ and SS of the Clover Bar WTP influent characteristics were analyzed. These samples were composite samples. The BOD₅ fluctuated between 200 and 400 mg/L, with a few spikes in excess of 500 mg/L. Similarly, the influent SS data varied between 200 and 450 mg/L, with a few excursions to more than 500 mg/L.

Over a five-month period the median BOD₅ and SS were approximately 300 and 350 mg/L, respectively. Table 1 summarizes and compares these data to the calculated northern camp wastewater strengths. The data show that the actual influent to the modular WTP was stronger than a pre-treated northern camp wastewater.

The process effluent temperatures varied from 4 to 13°C. At an HRT of 18 – 27 hrs, the average temperature loss going through the module was approximately 3°C.

Figure 2: Median effluent BOD₅ and SS concentrations - January 2002 to May 2002.

Module operating mode Operating a wastewater treatment plant in remote locations in an extended aeration mode satisfies a number of desirable attributes:

This process is more robust, less prone to process upsets.
Less operator skill and attention is required.
Less sludge is generated.

Plant start-up The plant was transported to the Edmonton Capital Regional Clover Bar wastewater treatment plant in late October 2001. It took one day to complete all piping and power hook-ups. Wastewater was then pumped to the treatment module at an initial rate of 1,200 US gpd (4.5 m³/d). Influent BOD₅ and SS concentrations averaged about 300 and 350 mg/L, respectively. After approximately three weeks, the effluent BOD₅ and SS concentrations were 23 and 25 mg/L. During this start-up period, the reactor liquid temperature varied between 13 and 9°C. Subsequently, the hydraulic rate was increased to 2,100 US gpd (~ 8 m³/d). This sudden hydraulic shock coupled with some power outages resulted in a deterioration of the effluent quality. By mid-December a stable effluent quality of less than 20 mg/L BOD₅ and SS was again achieved. It was decided to start analyzing data and record operating experiences in January 2002.

Figure 3: Median effluent concentrations for various flow rates

Operational history The plant was operated at three constant, distinct hydraulic modes:

2,700 US gpd (10.2 m³/d) from January 22 to March 17;
3,500 US gpd (13.2 m³/d) from March 19 to April 16; and
2,300 US gpd (8.7 m³/d) from April 18 to May 17.

It took approximately six weeks for a significant biomass to develop. Over the study period the average MLSS concentration varied between 2,000 and 2,700 mg/L.

Daily standard 30 minute settling tests indicated that, despite a very high SVI, excellent liquid solid separation was obtained.

Sludge production By assuming 80% of the sludge is active biomass, it can be calculated that 0.24 kg VSS are produced per kg BOD₅ treated when operating at a daily flow of 13.2 m³/d. This dropped to, 0.13 kg VSS at 8.7 m³/d. At 13.2 m³/d the module was no longer operating in the extended aeration mode but in the conventional activated sludge mode.

Sludge wasting During the 28-day, 13.2 m³/d flow rate period, 14.7 m³ of sludge were wasted. This represents 32.8 kg of solids wasted for 370 m³ treated. This amounts to 0.04 m³ of sludge wasted per m³ of wastewater treated.

Similarly for the 8.7 m³/d flow rate, the amount of sludge wasted was approximately 0.03 m³ per m³ of wastewater treated. The total sludge mass wasted during that 31-day period was approximately 15.4 kg.

Biokinetic™ effect After the sedimentation step the effluent passes through the Biokinetic units. These units serve as an additional liquid/solid separator, polishing the effluent by removing SS through filtration. The data show that the effluent polishing effect is approximately 5 mg/L SS.

Conclusions The following are the major conclusions of this study:

The treatment module was started successfully during the winter months.
Within a hydraulic operating envelope of 13.2 to 8.7 m³/d, the module consistently produced an effluent not exceeding a median concentration of 20 mg/L BOD₅ and 20 mg/L SS.
For design purposes, the module will produce the following median effluent quality:
- Less than 10 mg/L BOD₅ and 10 mg/L SS at 8.7 m³/d.
- Less than 15 mg/L BOD₅ and 15 mg/L SS at 10.2 m³/d.
- Less than 25 mg/L BOD₅ and 25 mg/L SS at 13.2 m³/d.
Sludge production ranged from 0.27 kg SS/kg BOD₅ at a hydraulic loading of 13.2 m³/d to 0.16 at 8.7 m³/d.
Beyond routine inspections and effluent sampling, the module requires minimal operator attention.

This article is a synopsis of a report Achieving a 20/20 Effluent from a Modular, Mobile, Wastewater Treatment Plant for Northern Camps – 150 days of Technology Demonstration by Dr. Norbert W. Schmidtke, P.Eng. Environmental Process Engineering Specialist, and Kevin Zhang, Wastewater Treatment Operations Specialist, Tanks-A-Lot Limited, Edmonton, Alberta. July 2002.

References 1. Cold Climate Utilities Delivery Design Manual, Economic & Technical Review Report EPS 3-WP-79-2, Environment Canada, Water Pollution Directorate, March 1979.
2. Imhoff & Fair, Sewage Treatment, John Wiley & Sons, pg. 43.
3. Fair & Geyer, Water Supply & Wastewater Disposal, John Wiley & Sons pg. 563.
4. US EPA Design Manual – On-Site Wastewater and Disposal Systems, October 1980.

Acknowledgements The authors are grateful for the role key individuals played in making this study happen:

Gordon Thompson, P.Eng, General Manager of the Alberta Capital Region Wastewater Commission who approved the project,
Claude Ouimette, Project Manager and his staff with OMI Canada Inc. responsible under contract to the Commission for the O & M of the Alberta Capital Region Wastewater Treatment Plant and
Zenith Moisey, P.Eng. of Tanks-a-Lot who provided the initiative and financial support for this project.

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