Background The domestic sludge contains a large number of nutrients such as nitrogen, phosphorus and potassium, but accumulates a large number of pathogens and organic pollutants such as parasites (eggs).The light particles can be prepared for flower growth by using sludge and adding inorganic powders including clay, quartz sand tailings, diatomaceous earth, and so on. This effectively reuses domestic sludge and avoids environmental pollution from domestic sludge.

Methods Each raw material was ground using an agate mortar before test to maintain the particle size of the raw material between 200 and 600 mesh. The particle size distribution of each raw material was measured using a Bettersize2000 laser particle size distribution analyzer. The compressive strength of lightweight particles was measured using an ATH-5000 spring tension tester. The microscopic morphology of light particles was analyzed using an EVO-18 scanning electron microscope. The product crystal analysis was carried out by XD-3 X-ray powder diffractometer.

Results The compressive strength of the light particles decreased from 7.47 to 2.33 MPa, the bulk density decreased from 1.63 to 1.11 g/cm³, and the water absorption rate increased from 33.33 to 63.67%, when the sludge content increased gradually from 0 to 100%. The compressive strength of the light particles increased to 7.35 MPa then began to decline, the bulk density of the light particles increased from 0.91 to 1.20 g/cm³, thus, the water absorption rate gradually decreased from 61.33% to 40.33%, when the contents of clay increased from 0 to 100%. Quartz sand tailings were to increase the content of the SiO₂ of the product, and improved compressive strength of the products. The products possessed strong adsorption with water absorption rate of 50%, by the porous structure of diatomaceous earth and the amount of organic matter evaporated in the sludge. The optimal addition amount of each inorganic powder reagent was determined using single-variable control method as domestic sludge 50%, clay 30%, quartz sand tailings 10%, kaolin 5%, diatomaceous earth 2%, Al₂(SO₄)₃ 3%, firing temperature 930℃, and holding time 50 min, the compressive strength of the light particles prepared under the optimal conditions was 4.0 MPa, the water absorption rate was 50%, and the nutrient mass fraction N 37.1 mg/g, P 12.5 mg/g, K 4.4 mg/g.

Conclusions The utilization rate of the domestic sludge is up to 50%, the compressive strength of the light particles is above 7.0 MPa, and the water absorption rate is 50%. The performance of the product particles is superior to the domestic and foreign equivalent products, and meets the vegetation growth requirements of flowers and the like, accorded with national standards GB/T 17431-1998. The conditions provide a simple and easy way to utilize sludge efficiently, and showing certain economic, environmental and social benefits.