Sustainable production of polyhydroxybutyrate biopolymers and cellulose microfibers from sugarcane waste

Abstract

Thermochemically pretreating sugarcane bagasse (SCB) and sugarcane leaves (SCL) at 121 °C generated fermentable sugars that were transformed into polyhydroxybutyrate (PHB) by PHB-producing bacteria. The SCB hydrolysate contained reducing sugars (25.0–26.1 g/L), which were mainly xylose (16.4–17.6 g/L) and glucose (7.8–8.0 g/L). The bacteria used glucose more effectively than xylose and glycerol did, as the maximum PHB contents (% cell dry weight) observed with glucose, xylose, and glycerol were 69.3 %, 16.2 %, and 21.4 %, respectively. After 72 h of incubation, Burkholderia cepacia ASL22 and Priestia megaterium ASL11, KKR5, and SRB3 converted 50 % of the SCB hydrolysate in E2 broth into PHB, and the maximum weight (1.97 g/L) and content (32.6 %) of PHB were obtained with B. cepacia ASL22. Strain ASL22 also grew on E2 agar, producing 56.0 g/L PHB when 10 % SCB hydrolysate and 0.3 % (v/v) glycerol were used as cosubstrates. Furthermore, combining alkaline treatment, xylanase hydrolysis, and NaClO₂ bleaching converted SCB and SCL into high-purity cellulose microfibers (CMF) with a low yield (31 %). After peroxide bleaching, alkaline treatment and sonication, the CMF yields ranged from 88.3 % to 95.1 %, but some lignin and hemicellulose remained. Thus, sugarcane waste can be processed biologically and physicochemically to produce value-added products, thereby reducing pollution.