Raw Water:
All water treatment begins with proper source selection. The raw water from Lake Huron provided by the Saginaw Midland Municipal Water Supply Corporation (SMMWSC) is second none. Once the raw water gets to the facility, it is routed through a 10-million-gallon ground storage tank. This tank not only provides us with a days’ worth of raw water storage, it allows heavier items to settle out. Raw water from the tank is then pumped through the filtration process’s only pretreatment step, strainers. The self-cleaning auto-strainers have screens with 250-micron (a micron is 1 millionth of a meter) openings which ensure large debris doesn’t make to the membrane filtration equipment.
Filtration:
The Bay Area Water Treatment Plant utilizes UF (ultra filtration) membranes. Membrane filtration doesn’t rely on a chemical and hydraulic processes to settle unwanted particles out of the water, instead they are physically strained out. The plant has eight filtration skids divided evenly into two trains. Each skid has 240 membrane modules. Every module has a pore size of 0.04 microns. It’s hard to visualize how small that pore size is but it is small enough that it provides a physical barrier to a wide range of pathogens like Crypto and Giardia.
Chemical Treatment:
After going through the membranes, filtered water is dosed with Sodium Hypochlorite for disinfection, Hydrofluosilicic Acid (Fluoride) for dental protection, and Phosphoric Acid for corrosion control. This treated water is then routed through 2 finished water tanks outside the plant. The finished water tanks are operated in series to ensure proper chemical mixing, allow for maximal contact time for disinfection, and provides on site storage of treated water. Once the treated water has achieved the appropriate amount of contact time, it is called finished water or tap and it is ready to be sent out into the distribution system.
Finished Water Pumping:
The plant utilizes a mix of high service or finished water pumps to move water from the finished water ground storage tank at the plant into the distribution system. The smaller pump is capable of moving upwards 5,600 gallons per minute (gpm), while the larger pump can move as much as 7,500 gpm. These pumps are able to achieve these flow rates at head pressures upwards of 65 psi. This is enough pressure to fill up the water towers found through out the water system. There are 7 water towers in service that represent almost 5 million gallons of storage, more than enough water to handle very large swings in consumer demands. The water system is also broken up into 3 different pressure zones; a high-pressure area west of I75, a low-pressure area in Linwood, and then there is the rest of the water system. These pressure zones require pumping stations and pressure reducing valves to regulator pressure. The water system relies on 3 different pumping stations to increase pressure, sustain pressure, and recirculate water.
Backwashes and Recovery:
As a membrane skid filters it forms a collection of suspended solids called a filter cake. After a period of time, this filter cake begins to hinder the filtration process and it needs to be flushed out with a process called a backwash. Air and water are used during this process to flush and clean particulates from the membrane surfaces. This backwash water is captured and sent through a recycling process that helps to limit the amount of waste water produced at the facility. The backwash water is sent through flocculation tanks where a coagulant called Aluminum Chlorohydrate is used to get small suspended solids to form larger, heavier particles called floc. This floc laden backwash water is then sent through parallel plate settlers to settle out the now heavier particles in the water. This settling process creates two different waters, a clarified water and a thicker water called sludge.
Residual Management:
The clarified water is routed back to the head of the plant and begins the filtration process all over again. In 2024, 90.8 million gallons of clarified water was recycled to the head of the plant. That volume of water represents 3.3% of our raw water flow in 2024. This recycled water is source water that didn’t need to be purchased and is an overall financial saving for facility. It also represents waste that was ultimately not generated, making the facility more efficient. The sludge on the other hand, is a waste stream intentionally generated by the facility. There is no getting around it, filtering unwanted particles out of the water creates a waste that needs to be disposed of. In 2024, 42.6 million gallons of sludge were created by the facility. This sludge is pumped off site to a dewater lagoon. The lagoon receives the sludge and decants off a water fit for discharge to a local water way through a NPDES permit. This volume of sludge represents 1.5% of the total production of the facility. This means that in 2024, the membrane filtration process used at the facility was roughly 98% efficient from the perspective of its water use.
Public Awareness and Water Stewardship:
Are you interested in visiting the water plant? If you are a customer served by the water plant, you are invited to tour the facility and see where your water comes from. Depending on the level of curiosity, an average tour takes about an hour to complete. Tours will be limited to 2 or 3 people at a time and will be given by one of the supervisors during normal hours of operation. If this sound like something you are interested in, send a request to BAWTP@baycountydwsmi.gov with “Tour Request” in the subject line. Due to the sensitive nature of the facility, site security and risk mitigation are always a concern. Please include your name, address, and phone number in your email. Once your email is received and your information is verified, staff will reach out to coordinate your tour.
Do you work in the water industry and would like to learn more about membrane filtration? Every year the Bay Area Water Treatment Plant partners with EGLE to host an annual membrane training class. This class is aimed at teaching attendees about the basics of a membrane filtration system. Tours are also available if you prefer a walkthrough with a supervisor who can directly answer your questions. Please send an email to BAWTP@baycountydwsmi.gov with “Waterworks Tour” in the subject line. Please include your name, address, phone number, operator ID, and your home WSSN in your email. Once your email is received and your information is verified, staff will reach out to coordinate your tour.