After larger particulates have been removed, influent is split between four primary clarifiers—essentially large settling basins. Here, chemical coagulants help mid-sized organic and inorganic particles to clump and settle.
So what’s removed? Chemical coagulants help to remove phosphorus from the influent, as well as heavier inorganic and organic materials, which settle to the bottom of the tanks and are removed for processing. Processed solids are used for fertilizer on area farm fields or disposed of in a local landfill. The settling process also helps fats, oils, and greases separate from the rest of the waste stream so that they can be removed, concentrated, and disposed of separately. Fats, oils, and greases enter the sewer system when poured down drains as well as from poorly maintained grease traps in restaurants and other businesses.
Aeration: Secondary Treatment
When mid-sized organic and inorganic materials have been removed, the influent is aerated to create an oxygen rich environment in which the right microorganisms can thrive, allowing for effective secondary aerobic treatment. Without aeration, secondary treatment and removal of any remaining solids is impossible.
The aerobic process that our wastewater treatment plant employs is great at cleaning the wastewater stream before it’s returned to Lake Macatawa, but it does little to remove most harmful chemicals and solvents. These compounds could potentially kill the microorganisms that do most of the work, effectively shutting down our plant—requiring an expensive re-seeding using activated sludge from another facility. To help eliminate these harmful compounds from the waste stream before they jeopardize our facility, the HBPW partners with businesses across the community for industrial pretreatment programs to dispose of these and other harmful waste products properly.
Secondary Treatment Part II
Remaining organic and inorganic solids settle to the bottom of the tanks and are removed. A large portion of the removed solids are returned to the aeration basins to replenish the microorganism populations performing the treatment and the remainder is disposed of as biosolids. These biosolids are processed and used for fertilizer on area farm fields or disposed of in a local landfill. Any floatables are skimmed from the surface and returned to the head of the plant for retreatment.
The microorganisms grown in the aeration basin form flocculant masses which allow for the settling of remaining solids.
In its final stage of purification, effluent is disinfected with sodium hypochlorite—bleach. This clean water is recycled to be used as coolant in our James DeYoung Generating Facility before being returned to Lake Macatawa.
By the time effluent reaches the disinfection stage of the wastewater treatment process, it’s already free of solid waste. However, sodium hypochlorite kills any bacteria that remain in the waste stream, including fecal coliform bacteria.
This year, our wastewater treatment facility maintained removal rates of 98% Biochemical Oxygen Demand (BOD), 96% of Total Suspended Solids (TSS), and 93% of phosphorous—all substantially better than are required by the EPA.