Wastewater is a combination of used water from domestic sources such as residences, and non-domestic sources such as industrial, commercial, and institutional facilities. Wastewater contains a number of different substances, most importantly Total Suspended Solids (TSS). Suspended solids in the wastewater, if not removed and discharged into the environment, can decay or break down naturally by consuming oxygen. This demand for oxygen commonly known as Biological Oxygen Demand (BOD) is a measure of how clean the wastewater is.
Wastewater Treatment
There are many reasons to treat the wastewater before discharging back to the environment:
- Marine life and aquatic habitat protection - Untreated wastewater can consume oxygen that is available for plants and animals and cause them to suffer and may even kill them.
- Recreation and quality of life – Untreated wastewater can affect swimming, sport fishing, boating, picnicking etc. by imparting undesirable colour and unpleasant odour to the receiving water.
- Health concerns – Untreated wastewater can cause disease causing microorganisms to enter into receiving water that we may use for drinking and recreation.
Wastewater is treated in many different ways. All kinds of wastewater treatment involve removing suspended solids and reducing BOD in the wastewater. Please read through the following steps to understand how wastewater is treated by the City of Abbotsford at the Joint Abbotsford Mission Environmental System Wastewater Treatment Plant (JAMES WWTP).
Primary Treatment
Primary Treatment involves mainly mechanical processes such as headworks and primary sedimentation that removes up to 40 percent of BOD and 60 percent of TSS from the wastewater.
Headworks
Wastewater that comes into the plant is pumped to the headworks area of the plant by three screw pumps. The headworks consists of screening and grit removal systems where large objects such as rags, sticks, plastics, stones and grit are removed from the wastewater, dewatered and sent to the landfill. The screened wastewater flows by gravity to Primary Sedimentation tanks.
Primary Sedimentation
Primary Sedimentation is performed in seven large open-air tanks. The wastewater is held in these tanks in a quiescent state for 2 to 4 hours. Lighter particles float and are skimmed off and are dewatered then sent to the landfill. The heavy solids (Primary Solids) that settle to bottom of the Primary Sedimentation Tanks are removed from the sedimentation tanks and sent to the Digesters for further treatment. The overflow, known as Primary Effluent, from these tanks goes to the secondary process for further treatment.
Secondary Treatment
Secondary Treatment is a biological process that removes up to 90 percent of BOD and TSS.
Trickling Filters and Solids Contact Tanks
Trickling Filters are large tanks that are packed with natural media such as rocks or synthetic media such as plastic plates. The packed media serve as a support structure on which naturally occurring microbes can grow and eat the dissolved organic material present in the wastewater. Wastewater is usually introduced at the top of the filter and treatment occurs as the wastewater trickles down to the bottom of the filter, hence the name Trickling Filter.
JAMES Plant has two rectangular tricking filters packed with synthetic plastic media. The Primary Effluent is pumped to the top of the filter and distributed over the plastic media plates where dissolved organics are eaten by the growing biomass creating larger particles that can be settled out in the Secondary Clarifiers.
Each Trickling Filter at the plant has a Solids Contact Tank. The function of Solids Contact Tank is to facilitate aggregation of finely divided microbes in the trickling filter effluent into heavier and easily settleable microbes. The trickling filter effluent and settled solids from secondary clarifiers are combined in this tank and aerated for microbes’ aggregation. The liquid flowing out of the Solids Contact Tanks flows into the Secondary Clarifiers.
Secondary Clarifiers
The JAMES Wastewater Treatment Plant has four circular Secondary Clarifiers, which are large open-air tanks where the fully grown microbes, having done their work of eating the organic material, settle to the bottom of the tanks as sludge (Secondary Solids). A portion of this sludge is returned to the Solids Contact Tanks as mentioned above and the remainder is thickened and then sent to the Digesters. The clear liquid at the top of the clarifiers, also known as Secondary Effluent, overflows to the next stage of treatment called Disinfection.
Disinfection
Disinfection is a process by which microorganisms present in the wastewater are killed, some common disinfection methods are chlorine, Ultraviolet light or Ozone.
The secondary effluent is pretty clean, but it still contains large number of invisible harmful microorganisms that need to be destroyed before discharge into the Fraser River. To destroy the microbes, the JAMES Wastewater Treatment Plant currently practices disinfection by passing the wastewater through banks of UV bulbs.
Treated Wastewater Discharge
The treated wastewater is then discharged by gravity or pumping into the Fraser River via a 1200 mm diameter outfall pipe.
Digesters
There are three digesters at the JAMES Wastewater Treatment Plant. They are large enclosed tanks where the settled sludge from primary sedimentation tanks and secondary clarifiers are digested in the absence of air or oxygen. This digestion process greatly reduces the organic content and odour of the sludge. The end products of the digestion process are methane gas and “Class B” Biosolids.
The methane gas is used as a fuel to produce heat at the plant. Biosolids are dewatered by centrifuges and the dewatered biosolids are temporarily stored on site before land application.
Everything that you put down your toilet and household drain ends up in our sewer system.
Flushing non-flushables can cause sewer blockages, damage pipes and treatment systems, backup sewers in your home and result in sewer overflows that harm the environment. This could mean expensive repairs for you and often, increased operations and maintenance costs to the collection system and wastewater treatment plant.
Non-flushable items include Fats, Oils and Grease (FOG), “flushable” wipes, dental floss, and many more. View the Sewer Savvy Brochure to learn more about what not to flush or put down the drain!
The existing 600mm diameter steel siphon sanitary main, from Mission to the JAMES Wastewater Treatment Plant (WWTP) in Abbotsford, was installed across the Fraser River in 1982, downstream of the Mission Bridge.
The City of Mission has completed a new 900 mm sanitary sewer pipe, in parallel with the existing main, to increase capacity and provide redundancy to the existing forcemain.