ABSTRACT
BACKGROUND: Different bulking agents are used in the compost of dewatered sludge (DWS). The aim of this study has been using of indigenous bulking agents (IBAs) in the enhancing of the DWS class of municipal wastewater from class B to class A and complementary stabilization of it for production of green manure in Sari city, Iran. METHODS: Three IBAs including the Saccharum Wastes (SW), Citrus Purning Wastes (CPW) and Phragmites Australis (PA) from eight IBAs were selected to be compared with the sawdust (SD) that was as a control bulking agent. Five turned windrow piles were constructed on a full scale and on base of optimal C/N equal 25.All experiments were performed on the base of the standard methods on initial mix and final compost. RESULTS: Among five windrow piles, P5 was been the best pile with a weighting ratio of DWS to IBAs (DWS: SW: CPW: PA) equal 1: 0.2: 0.24: 0.28. Pile P1 with weighting ratio DWS: SW equal 1: 0.6, Pile P3 with weighting ratio DWS: PA equal 1: 0.84, Pile P2 with weighting ratio DWS: CPW equal 1: 0.73 and Pile P4 with weighting ratio DWS: SD equal 1: 0.57 were placed in the next rounds. The results showed that the class of DWS enhanced to Class A for about 80 to 97 days and complementary stabilization of DWS by IBAs was done well and produced green manure in term of organic matter, potassium, germination index, PH, C/N and electrical conductivity had reached to the Grade 1 of Iran's manure 10716 standard and in term of phosphorus and moisture had reached to the Grade 2 of this standard. Also heavy metals were below the maximum permissible of standards. CONCLUSION: Using of IBAs, had a higher efficiency than the control bulking agent (sawdust) in enhancing sludge class and its stabilization, so that using of them in combination (mix of IBAs) had the highest efficiency and respectively, Saccharum Wastes (SW), Phragmites Australis (PA), Citrus pruning wastes (CPW) were placed in the next round, and sawdust was placed after them. By adding suitable IBAS, with an optimal ratio in turned windrow method, the class of DWS of sari WWTP enhanced to Class A and complementary stabilization of DWS has been well done and the produced green manure has been reached to agricultural standards and can be safely used in agriculture.