You already know that your drinking water comes from Quabbin Reservoir and your wastewater goes to the ocean via Deer Island, both courtesy of the Massachusetts Water Resources Authority (MWRA). You may recall the Boston Harbor Clean-up, which happened in the late 1980s and early ‘90s. But do you really understand what happens to your wastewater?

A group of GDN members and others found out, thanks to an MWRA tour of the Deer Island Treatment Plant in September, hosted by Dede Vittori of the MWRA. MWRA engineer Charlie Tyler explained the process for treating the billion gallons of wastewater that come to the Deer Island plant. He then led the group on a tour of the plant through pipe galleries, around those giant eggs that we see flying out of Logan Airport, and over the roofs of the gigantic treatment tanks.

Sewage treatment is a process of managing natural micro-organisms that digest the sewage, not unlike managing fermentation in a brewery. Undigestible solids (including facial tissues and wet wipes!) are first removed, settling is allowed to happen in huge primary tanks, and the separated liquid is conducted to secondary tanks where air is introduced to foster the desired bacterial action over several days. The much cleaner effluent is disinfected, and finally it travels through 11 miles of tunnel to diffusers on the bottom of the ocean. The residual solids are routed through the egg-shaped sludge digesters, for stabilization, then disinfected, dried and made available as solid pellets for use as fertilizer. (The MWRA has a regional program to reduce toxic materials from entering the sewerage system, keeping the levels of these toxics in the resulting fertilizer from exceeding regulatory criteria.)

Most of the methane produced in the treatment process is captured for use in the process, and wind turbines on the site help to reduce the electrical energy needed by the previous plant have been preserved, and the perimeter of Deer Island (actually a peninsula) is public open space. In all, an impressive and educational experience.