Effective utilisation of trickling liquid discharged from a bio-trickling filter as a moisture conditioning agent for composting

• During composting process, feasibility of adding trickling liquid was investigated.
• Adding trickling liquid could enable zero discharge of trickling liquid.
• Adding trickling liquid accelerated the decomposition rate of organic waste.
• Adding trickling liquid promoted compost maturity.
• Adding trickling liquid increased the nitrogen content of compost products.

Primary fermentation experiments were carried out investigating the disposal and reuse of trickling liquid discharged from a bio-trickling filter as a moisture conditioning agent. The liquid was mixed with food waste and mushroom bran. Compared to the addition tap water (TW), the addition of trickling liquid (TL) was found to accelerate the decomposition/fermentation rate of organic waste, which is defined in terms of enhancement in heat generation and waste mass reduction. The acceleration effect may be due to the activity promotion of heterotrophic bacteria induced by the addition of TL containing high level of ammonium. The addition of TL also promoted compost maturity based on the evaluation indices. The carbon–nitrogen ratio, Q2/6, and Q4/6 of the TL treatment were 15.3, 10.7, and 7.6, respectively. These values were 8.9, 4.3, and 3.6 lower than those in the TW treatment after 15 d of primary fermentation. The germination index of the TW treatment was 22.3% lower than that of the TL treatment (79.4%), which met the criteria (80%) for maturated composting product. Furthermore, a nitrogen mass calculation indicated that mass reduction of nitrogen of the TL and the TW treatments were −9.6% and 12.2%, respectively. Therefore, reusing TL as a moisture conditioning agent for organic waste composting could enable zero discharge of TL, promote maturity, and increase the nitrogen content of compost.