Evaluation of Membrane Systems
Evaluation and Documentation of Membrane Systems for Latrine Pit Waste Management in India
We know that one of the grand challenges of solving the global sanitation crisis is not only getting a toilet to everyone, but emptying latrine pits/septic tanks when they fill and where there is no sewer and space to build another pit. Anecdotal observation of the pit emptying process show that the vast majority of waste removed from pits in both Africa and India is dilute. This was counter-intuitive to initial thoughts as the sludge was assumed to become thicker with age resulting in difficulty in removing aged solids from pits. The finding of dilute solids initiated research undertaken by Water for People and Mott McDonald into the physical characteristics of pit sludge and the use of the ‘ball penetrometer’, which takes profiles of the sheer strength of the sludge within the pit. This work revealed that many pits are filling up with water, not dense sludge, due to infiltration and introduction of water during use. This turned the thinking on its head and switched focus to minimizing water within a pit.
For pour-flush latrines, water is only needed to flush excrement the short distance from the bowl to the pit and for anal cleansing (squat toilets), after which it becomes a hindrance. Water fills up pits quickly, makes transport more costly, and invokes the need for large expensive wastewater treatment plants whose primary purpose is to separate the water from the solids. Improving water management to keep water out of the pit could have a huge impact on every subsequent part of the value chain by keeping solids content of the sludge high.