Every day, water treatment plants release a sludge quite a large amount. Only counting for Thu Duc and Binh An Water Purification Plants (HCMC), the amount of sludge discharged is estimated at 250 tons of dry sludge / day. Currently, the solutions to treat sludge in the world as well as in the country are mainly used to replace a part (5-10%) of alominosilicate originating materials in cramic technology (brick burning, cramic burning, etc.), as an unburnt material with the primary bonding agent is Portland Cement. In addition, there are a number of other solutions to treat such as waste disposal, alum recovery, making composite, landfilling, but it is not economic efficiency and environmental pollution.

According to Associate Proffessor, Dr. Do Quang Minh, currently, no research in the country has been done on the production of backfilling materials based on sludge geopolymerized materials and alkaline active substances. This is also a relatively new treatment method in the world.

After more than a year of research, the group has successfully tested and proposed the process of manufacturing backfill materials from the water plant sludge. Accordingly, industrial waste sludge, fly ash, caustic soda (99.8% NaOH) are the raw materials for the production of leveling materials using geopolymer technology.

Waste sludge is collected from water plants with humidity of 30-40%. Mix the ingredients at the rate of 40% fly ash, 60% sludge and 10% NaOH 10M solution, then put into the extruder and dried in a rotary barrel dryer or drying chamber. The above blending will reduce the drying stage of sludge, because when mixed according to the above ratio, the mix has a moisture content of 10 - 15%, suitable for forming plastic shapes. Materials are tested on production equipment line of Trung Hau Company. Output products are checked for mechanical properties to ensure quality. Products with compressive strength above 3.5Mpa, water absorption, softening coefficient all meet TCVN: 6477: 2016 and do not emit toxins into the environment.

According to Dr. Minh, in order to produce the above-mentioned fill material, it is possible to apply the technological process as proposed by the research team (mix the ingredients according to the above ratio, put into the mixer, then extrude and dry in the drum to make the final product). In addition, it is possible to apply backfilling material production depending on the existing production lines and technology of each company.

Currently, the water treatment plant costs about 1.4 million VND / ton for the environmental company to treat the sludge. Using the above method, the cost will be lower (about 200,000 VND / ton, not including the cost of investment in factories, machinery and equipment), and at the same time solve the waste storage space.

The research project was accepted by the Ho Chi Minh City Department of Science and Technology of by the end of 2020.