The Masinda Starch plant is a small scale processing plant located in a fairly isolated rural area. Cassava is collected by ox-cart from the surrounding farmers and transported to the plant. It is then weighed, washed, and grated. After it has been grated into a thick pulp like substance, water is added and the starch is separated from the fibers by sieving. The water starch solution then passes through a sedimentation channel. After the channel is drained there remains a layer of starch at the bottom which is removed and dried. Once it is dry, it is milled and packaged.
The main issue with the wastewater, which contains mainly water and starch, is its high BOD (biological oxygen demand). If the water is directly discharged to the near by river, the decomposition of the organic matter (starch) will use up the oxygen in the water killing aquatic life. Another major issue is that the current wastewater system was designed for production rates of two tons of fresh cassava per day and the plant is currently running at about 8 tones of fresh cassava per day. What further aggravates the situation is that the currently system is also heavily clogged with solids. Oh, it also smells pretty bad from the fermination going on.
As a temporary solution we have begun to build a berm 15m from the river to contain the overflow. The water flow through 15m of soil should adequately clean the infiltrated wastewater before it enters the stream. We have also directed overflowing pits to a large recently dug dirt pit (see picture above).
After meeting with one of the people from IITA who was involved with designing the original system, the preliminary long term solution that we came up with was:
1. Develop a maintenance plan for regularly cleaning out the system, including composting pits for waste organic matter
2. Use screens to prevent larger debris from entering and clogging the system
3. Add power made from the Moringa tree into the large pits to act as a coagulant (enabling more solids to be removed)
4. Add limestone powder to smaller pits to neutralize the acidity of the water
5. Direct water to adjacent cassava field after smaller pits
6. Direct overflow from cassava field to a low lying vegetated areaThis vegetated area can also be enhanced with plantings of water purifying and absorbing plants. A berm should also be created downstream of the vegetated area to prevent potential contamination of hand dug well.
Click on image to see full size
I am currently in Lilongwe researching the details of this plan. The other thing I wanted to look into was the viability of using the biogas created from the settling pit. Any comments, questions or suggestions are welcome.