Converting Waste Agricultural Biomass into a Resource - UNEP

Small perforated plastic bottles with pyrolyzed rice hull (top) are placed inside
larger perforated bottles (bottom) to form DEWATS' microbial support system.
DEWATS Project 229
The project is a form of decentralized wastewater treatment system
(DEWATS) but it could also be part of a centralized system. It is about treating
the effluent from septic tanks, which consists of an anaerobic filter, an aerobic
attached film reactor, and an algal pond. The system from employs waste
materials as components, which may lower the cost. Septic tanks made from
recycled plastics are recommended. The anaerobic filter reactor can either
made of waste plastics or concrete. It could be configured as upflow,
downflow, or baffled reactor. The microbial support materials are made up of
waste biomass residue (rice hull or coconut coir dust, as is or pyrolyzed and
bound together by melted waste plastic). The aggregates are placed inside
small perforated plastic bottles, which are in turn placed inside large
perforated bottles (gallon sized mineral water bottles). The large bottles are
stacked in the anaerobic tank. The support structures are made of waste
plastics.
Figure 1. Anaerobic filter reactor
The aerobic attached film reactor is similar to the anaerobic tank. It is also
provided with microbial attachment system made of waste plastic. Perforated
mineral water bottles (400 to 600 ml, top and bottom cut open) are welded
side-by-side standing up. Two small-perforated plastic bottles are placed
inside. The small bottles contain cut corrugated sheets (used cell phone
cards, aluminum cans, tetra-pak, etc.) Two assembled pieces occupy the
space near the sides of the tank (25% of total volume).
Aeration is provided at the bottom of the elevated assembly. The structural
support is made of recycled plastics. Using microbial support system is a form
of process intensification. Since septic tank effluent is low strength
wastewater, it cannot support and maintain the growth of free-floating
microorganisms. The microbial support system provides the biofilms that
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