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.

Current Work

The Water For People in India is working with partners WASH Institute (WASHi) and Population Services International (PSI). Funding for the development of solids separation technology to be used during pit emptying came from the Bill and Melinda Gates Foundation. The program researched solutions to minimize the water in solids. Relatively quickly two devices were developed based on membrane filtration. The effluent quality is high (meaning low percent solids), as is the solids quality (high percent solids) and the technology appears to be affordable and commercially available. The components of the membrane systems are:

The Pit Life Extender (for pit liquid removal and discharge)

This unit is designed to remain permanently with the pit. It removes and filters wastewater straight from the pit and treats it so as to enable the effluent to be discharged it into a nearby drainage channels. The solids remain in the pit.

It has given test results of BOD 19 mg/l and TSS 15 mg/l, which meets India discharge standards. The filter is capable of discharging at 1.2 l/min, which is more than sufficient for a household which uses 20 to 50 liters of flush water per day. WASHi estimate the selling price (with profit) would be Rps 4,300 ($65)

The Mobile Treatment Unit (for pit emptying, solids separation, and liquid discharge)

This mobile filtration unit is mounted on the back of a pick-up truck. It pumps out wastewater from the pit into a small collection tank mounted on the pickup. The liquids and solids are separated in the tank using a membrane based filtration system. The solids are dewatered in-situ via a small centrifuge and this removes the need for hauling dilute wastewater from the pits to the treatment plant. The liquid effluent has an average BOD of 19 mg/l and TSS 15 mg/l, which meets India discharge standards, and is discharged to the local storm drainage system.

The mobile treatment unit flow rate is higher than the pit life extender. It is capable of processing 3000 l/hour. The cost for the mobile treatment unit alone is Rps 350,000 ($5000). Including the pick-up, the total cost is Rps 900,000 ($13,000), which is about 75% the cost of a standard tanker truck.

All the technical and research aspects behind these membrane based solutions have been undertaken by WASHi, PSI and Water For People in Dindigul (Tamil Nadu), South India. The research was led by Dr. Marriappan of WASHi, a wastewater treatment expert.

Objectives of this ToR

Before Water for People, PSI, and WASHi proceed further to replicate and commercialize these new technologies, we want to ensure that we have done sufficient pilot testing, stress testing, and market testing. To this end, Water For People desires the assistance of a wastewater treatment specialist that can peer review our work in the field. The tasks we wish to accomplish include:

  • Evaluate the Pit Life Extender and Mobile Treatment Unit in service in 3 to 5 locations.
  • Validate the results produced by WASHi.
  • Review the technology performance, availability, ease of operation and maintenance, availability (and cost) of spare parts, and robustness.
  • Review the cost model (Capex and Opex) and produce a bill of quantities and accurate cost estimates (Capex) for the production of 100 Pit Life Extenders and 10 Mobile Units.
  • Water For People is particularly concerned about the longer term durability, cost and ease of maintenance. If the filters require replacement on a frequent basis it is likely to prove less attractive to potential customers. If the filters can be easily bypassed when clogged, it may result in untreated effluence being discharged (which is the current situation).
  • Produce equipment layouts, general specifications, and process flow diagrams of the two technologies so as to allow replication by other organizations.
  • Develop a list of equipment vendors and integrators.
  • Write a brief report/feasibility study for scaling and commercialization that identifies any technical fatal flaws, shortfalls, operation and maintenance challenges, and further research questions which need to be addressed before proceeding with further development work.

Questions to be Answered

  • Are the units capable of treating the effluent to the quality reported?
  • Are the results provided by WASHi valid and replicable?
  • Are there supply chains for spare parts and availability of replacement filters and other equipment?
  • What are the cost of producing the two types of units?
  • What are the expected capital and operational costs (including long-term maintenance needs including periodic membrane cleaning) of the two units?

Evaluation Methodology

The evaluation will involve travel to Dindigul and working with Dr. Marriappan and Water For People for one to two weeks. WASH I will be able to guide the consultant and provide access to field visits, equipment suppliers, and independent water quality testing labs.

Expertise required

  • Experienced wastewater process engineer with a good working knowledge of membrane filtration for wastewater
  • Experienced in wastewater effluent and solids testing
  • Experienced in producing technical reports and cost estimates
  • Willingness and ability to travel to South India to work in collaboration with the WASHi and Water For People in undertaking the evaluation (a visa is required to travel to India and takes several weeks to obtain)

Reporting requirements

Presentation of main findings, with question and answer session, to be given the Water For People, WASHi and PSI staff members.

A report containing all findings, technical drawings, bill of quantities and recommendations relating to completing the given objectives. To be provided in electronic form to Water for People, WASHi, and PSI.

Dates and Deadlines

To be mutually agreed upon.


Applications will be accepted until the position is filled with the right participant(s). If you have any questions, please contact volunteers@waterforpeople.org.

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