By Cezar Tigno
Web Writer, ADB
Environmental engineers have devised a decentralized wastewater treatment system using scrap plastic water bottles, rice hull, and other solid wastes. Pilot-test results are positive, but replication and upscaling remain challenging. Will this new technology from trash help solve the sanitation and wastewater problems in local communities?
Trash Technology: These recycled plastic bottles contain biomass residues that can turn murky water into clean water. |
A team of engineers have taken garbage recycling up another level with a new low-cost wastewater treatment technology straight from the trash bin.
“Our project aims to solve sanitation problems and environmental pollution caused by improper sewage disposal using a low-cost decentralized wastewater treatment system (DEWATS). We used solid waste materials to build it,” says Wilfredo Jose, a chemical engineer from the University of the Philippines, and the inventor of the technology.
The project, under the ASEAN University Network-South East Asia Engineering Education Network (AUN/SEED NET), is funded by the Japan International Cooperation Agency (JICA). Jose, together with Nguyen Thi Du from the Hanoi University of Technology and Makoto Shoda from the Tokyo Institute of Technology, make up the project implementation team.
The state-of-the-art technology at reasonable costs, resulting from the use of local materials, has made DEWATS applications popular in the developing world.
Jose’s invention, in particular, uses biomass residues, such as rice hull, waste wood, and dust from coconut fibers (called coconut coir dust), and solid waste materials such as plastic bottles, used phone cards, and aluminum cans—all available in most garbage dumps.In the Philippines, household wastewater contributes to 48% of water pollution. Often, household septic tanks are not emptied of effluent until they overflow. Even when emptied, effluent is not treated, causing waterborne diseases.
While the country’s 2004 Clean Water Act mandates that urban communities be connected to a sewerage system within 5 years, a staggering 94% of urban areas still have no sewerage system to connect to, posing a big challenge to the government. In rural areas, the Act calls for the proper disposal and treatment of septic tank effluent.
Jose says, “Septic tanks alone are inadequate for managing the country’s wastewater. They should not be treated as wastewater receptacles, and effluent must be treated at all costs.”
Currently, however, septic tanks have no capacity to treat raw sewage. And while many options for wastewater treatment are available, they cost higher in terms of capital investments, and operations and maintenance. This is where the DEWATS comes in as a viable alternative solution.Small perforated plastic bottles with pyrolyzed rice hull (top) are placed inside larger perforated bottles (bottom) to form DEWATS' microbial support system. |
The DEWATS is a plastic septic tank connected to an anaerobic reactor, an aerobic reactor, and an algal pond.
Septic tank effluent is filtered in the anaerobic and aerobic reactors—chambers where complementary chemical reactions take place to remove much of the wastewater’s filth. These chambers have “microbial support systems” that are capable of turning murky water into clean water.
The microbial support system for the anaerobic reactor consists of “pyrolyzed” waste biomass residue, and small and large perforated plastic bottles. Basically, the biomass residues, composed of rice hull or coconut coir dust that has undergone pyrolysis (a process of decomposition using heat), are bound together by melted waste plastic, and placed inside small perforated plastic bottles. These small bottles are then placed inside larger gallon-sized perforated bottles, and stacked in the anaerobic chamber.
Similarly, the microbial support system for the aerobic reactor uses solid wastes such as cut-up phone cards and aluminum cans, placed inside small perforated plastic bottles. They are then placed inside larger perforated plastic bottles, and lined-up near the tank’s inner walls. Low-cost blowers or air pumps at the bottom of the tank improve the water’s physical and chemical make-up through another process called aeration.
Clear water coming from these reactors is then discharged into the algal pond, lined also with waste plastics, to remove nitrogen and phosphorus nutrients, and increase the water’s pH-level to eliminate coliforms.
The project team constructed a pilot-scale system that could treat one cubic meter of wastewater. “We tested it using wastewater from a banana chip manufacturing plant, and found it capable of removing up to 99.59% of wastewater pollutants,” Jose said.
Ms. Nguyen Thi Du tinkers with the anaerobic filter reactor. |
One drawback of the DEWATS is that it is not large enough. The pilot-scale system could only treat one cubic meter of wastewater at a time. The septic tank would also require de-sludging every two or three years.
But the benefits that the DEWATS offers far outweigh these shortcomings. The system costs less than conventional septic tanks, and can last for many years. It can be used for both centralized and decentralized systems, as it can easily be reinstalled in other sites. More importantly, it solves both the wastewater management problem and the problem of solid waste disposal.
While the technology is sound, low-cost, and durable, however, there is another downside to the DEWATS. “From our experience, constructing the DEWATS is very labor-intensive,” Jose stressed.
Preparing the solid waste materials in usable form—perforating plastic bottles, processing biomass residues, and generally constructing the DEWATS—proved to be painstaking tasks for the project team. “But for small communities, where processing areas for waste materials can be established, the DEWATS can be easily replicated and could become a source of community livelihood,” the project team recommends.
On a much larger scale, local government units can be responsible for the construction, and operations and maintenance of the technology.Initially, the project drew a large interest among local government units and small-scale industries. However, lack of funding hindered actual applications. At present, the project team is conducting experiments with a similar system for wastewater from the food industries.
Jose said, “We have to let people know of this technology. The plastic septic tank has been available in the Philippines since 1997, but it has not been widely used. It is time to promote this environment-friendly product.”