Produção de biogás em resposta ao pré-tratamento químico e reúso do liquor negro aplicado aos resíduos de aparas de grama

Abstract

Alkaline pre treatment is commonly applied to lignocellulosic biomasses to solubilize lignin and release compounds that are easily degraded in anaerobic digestion. The main disadvantage of this method is the generation of toxic and alkaline effluent (black liquor) that makes pre-treatment more expensive. The reuse of black liquor as a solution for alkaline pre-treatments appears as an alternativeto reduce the consumption of water and chemical reagents in the process. The objective of this work was to evaluate the effect of the alkaline pretreatment applied to the waste grass clippings (WCG) and the efficiency of the reuse of black liquor for subsequent pretreatments, focusing on the production of biogas. Solutions of potassium hydroxide (KOH) and sodium hydroxide (NaOH) with concentrations of 1% and 5% were used, which were combined with RAG for 12 hours at room temperature (25 ° C). The collection of the black liquor was carried out after the separation of the phases (solid and liquid) and the pre-treated WCGwere washed to neutral pH to be used in the Methane Biochemical Potential (BMP) assays. The PBMof WCGwas 245 LNCH4 kg VS-1and after pretreatment with 1% and 5% KOH it went to 294 and 362 LNCH4 kg VS-1. The same effect was obtained with the application of 1% and 5% NaOH solutions that resulted in BMPof 332 and 323 LNCH4 kg VS-1, respectively. With the reuse of the black liquor, it was possible to carry out six new pretreatments and the sum of the biogas production potential (BPP) of KOH 1% and 5% was 2.650 and 3.LNCH4 kg VS-1. Likewise, the sumof the BPP of the pretreatment with 1% and 5% NaOH was 2.739 and 3.106 LNCH4 kg VS-1and indicated an 83% reduction in the demand for reagent. Based on this, it is estimated that the reuse of black liquor from 1% pre-treatments would have the capacity to generate 93 to 140 LNbiogas kg reagent-1whereas the 5% pre-treatments would be from 43 to 57 LNbiogas kg reagent-1. In this sense, the black liquor from the 1% pre treatments results in a higher PPB with only 1/5 of the reagent mass added in the process, which reduces the costs of pretreating the RAGs for the production of biogas. Among the pretreatments, NaOH showed greater potential for biogas production and lower cost of applying the method.