By Jim Dartez
Old municipal and industrial wastewater lagoons have the tendency to build islands of sludge at various locations around the lagoon. It is most common for older lagoons to build such islands wherever wastewater enters the lagoons. Of course, this is because the solids entering the lagoon have enough weight to fall out of the water as flow velocity is reduced, so the solids pile up just after entering the lagoon. Sometimes these sludge islands will build very near a surface aerator, because the violence of the aerator will either drop sludge out after lifting it, or because of the violent horizontal mixing of the aerator forms sludge piles near the aerator itself. Of course, sludge buildups along the bank are also very common because of the same horizontal mixing or due to predominant winds causing sludge buildup at the lagoon edges or banks.