RECYCLING WASTEWATER SLUDGE FROM MELAMINE-COATED PAPER FACTORY FOR AGRICULTURAL USE

This research aims to study the characteristics of adhesive sludge from a melamine-coated paper factory after dewatering and investigate the potential of adhesive sludge for agriculture use as fertilizer pellets. The adhesive sludge was collected from the final sedimentation pond, where the moisture content exceeded 70%. To prepare the sludge for pelletization, it was dewatered using a centrifuge until the moisture content was reduced to 15-20%. The sludge was then evaluated based on pH, organic matter content, Total N, P, K, and heavy metal contents. All parameters met the material standards for fertilizer production set by Department of Agriculture, Thailand [1], indicating the sludge’s potential as a fertilizer or soil conditioner. Fertilizer pellets were produced by mixing the sludge with organic or chemical fertilizers in various ratios (7:3, 6:4, and 5:5 by weight) and tested by cultivating Chinese morning glory. The experiment showed that the optimal ratio for mixing chemical fertilizer with adhesive sludge was 5:5, which have the most nutrients in fertilizer pellets such as Total N P K and Organic matter that produced the highest fresh weight and plant height of Chinese morning glory. Statistical analysis using Completely Randomized Design (CRD) and one-way ANOVA, conducted with SPSS showed no significant difference in the height, leaf size (width and length), root length, trunk circumference, and number of leaves of Chinese morning glory between non-mixed sludge and non-mixed organic fertilizer pellets. These results indicate that organic fertilizer pellets can be substituted with sludge fertilizer pellets. Furthermore, substituting organic fertilizer pellets with sludge-based pellets and reducing chemical fertilizer usage through a 5:5 sludge-to-chemical fertilizer ratio was feasible without compromising plant growth. No significant difference at the 95% confidence level was observed, indicating equivalent performance between non-mixed chemical fertilizer pellets and those mixed with adhesive sludge. This finding suggests that adhesive sludge could mitigate chemical fertilizer dependency, lowering costs and preventing soil degradation. Although formaldehyde and heavy metal contents in Chinese morning glory may be influenced by cultivation methods and environmental factors, the levels remained within the food safety standards established by the Ministry of Public Health’s, Thailand [2]. Despite meeting safety standards, it is recommended to prioritize using sludge-based pellets for cultivating ornamental plants or flowers, as this application reduces concerns regarding potential formaldehyde and heavy metal accumulation in edible crops. These results highlight the feasibility of recycling adhesive sludge as an eco-friendly and cost-effective agricultural resource.