Estimation of the self-purification capacity of biofilm formed in domestic sewer pipes

To estimate the self-purification capacity of sewer pipe, six different types of concrete blocks were installed in a domestic sewer pipe for nine months. The concrete blocks used were plain, grain, porous, and wet concrete (no-hole, or perforated with holes of d = 1 or 12 mm). After a 79-day exposure to sewage, a heterogeneous biofilm formed on the surface of each block. The self-purification capacities of the blocks were estimated by measuring the decrease in substrate concentration in artificial sewage. The analyzed substrates were dissolved oxygen (DO), total organic carbon (TOC), NH4+, and NO3−. Wet concrete with holes (d = 12 mm) showed the highest substrate consumption rates: DO = 460, TOC = 480, NH4–N = 87, and nitrogen as NO3–N = 170, in mg substrate/(m2 h). These results indicate that sewers have a considerable potential for removing organic material and nutrients, and modification of sewer surfaces may increase these activities.