A wastewater plant primer

By Ezra Blair - November 3, 2005

Wastewater treatment plants, like the Oak Bluffs plant are high-tech and complicated. They are science laboratories but on a massive scale, and each one is a little bit different.

While the engineering and science behind the Oak Bluffs wastewater plant are complex, the plant's basic functions can be described in several simple steps.

Wastewater from homes and businesses tied into the system flows to a pump station at the foot of School Street.

The wastewater is then pumped into a grinder pump at the wastewater plant. The grinder pump breaks up all the solid materials in the water.

The wastewater is then pumped into a series of sequence batch reactors (SBRs), high-tech, aerated tubs where microorganisms consume the organic material floating in the water. After a set amount of time, the oxygen that is fed into the tank is turned off. This allows the microorganism, and any solid matter to settle to the bottom of the tank where it can be removed and dewatered.

The clear effluent that is left on top of the sludge in the SBR is then pumped off to a special sand filters to remove any particulate that is left over. From the sand filters, the water is pumped through an ultraviolet disinfecting unit. The machine shines ultraviolet light through the water which destroys any viruses or pathogens that could be present.

The purified water is then gravity fed out of the wastewater plant to Veira Park, where a pump station pumps the water to Ocean Park where it goes into a leaching field to reenter the groundwater.

If Oak Bluffs voters approve the $1 million for a primary clarifying unit, the new equipment would be installed before the SBR units. The primary clarifier would remove oils, fats, and grease, which have caused problems in the other parts of the system.

Joe Alosso, Oak Bluffs wastewater plant superintendent, said that grease decreases the efficiency of the microorganism in the SBR units, clogs the sand filter, and coats the ultraviolet lights.

He said that a primary clarifier would also remove sand, silt, and other items that currently settle to the bottom of the SBR tanks and have to be shoveled out by hand.