Sugarcane vinasse is one of the most generated wastewaters in the bioethanol distillery, and one liter of bioethanol production could generate around nine to fourteen liters of sugarcane vinasse (España-Gamboa et al. 2011). Vinasse contains a lot of harmful substances, such as phenols, polyphenols, and heavy metals, as well as significant levels of organic content and dissolved solids. Its characteristics of being acidic (pH of 4.30–4.55), dark brown, and having a high chemical oxygen demand (COD) concentration (28.5–85.0 gCOD/L) are necessary to be a concern since the phytotoxic and recalcitrant compounds in the sugarcane vinasse could negatively affect the organisms at disposal sites (Chai et al. 2021; Kiani Deh Kiani et al. 2021; Takeda et al. 2022). Disposing of untreated/partially treated vinasse on land or groundwater could cause a profound environmental impact. Thus, the bioethanol industry has adopted some technological applications such as fertigation (Carpanez et al. 2022), physico-chemical (Hoarau et al. 2018), and biological treatments (Silva et al. 2021). Fertigation using sugarcane vinasse is commonly applied due to the increase of crop productivity without complex technologies for its management; however, its uncontrolled practice can cause soil salinization, water sources contamination, and bad odors release (Fuess and Garcia 2014).
The coagulation/flocculation method is the most common chemical treatment technology, especially as a pre-treatment process for the vinasse. During the coagulation process, colloidal and finely divided suspended matters are facilitated in the aggregation to generate larger flocs that can subsequently be separated through sedimentation or filtration to clarify water from impurities (Abujazar et al. 2022). The coagulation-flocculation process using poly-γ-glutamic acid combined with sodium hypochlorite and sand filtration could reduce 70% and 79.5% of the turbidity and COD concentration, respectively, in the tequila vinasse treatment (Carvajal-Zarrabal et al. 2012). Besides, FeCl3-involved coagulation post-treatment for biologically treated distillery wastewater could achieve high decolorization efficiency (Zhang et al. 2017a). It was discovered that the ferric coagulant preferentially interacts with the aromatic compounds and melanoidins through surface complexation, charge neutralization, or both. Additionally, to reduce the coagulant dosage and increase the degradation potential, Moringa oleifera seed extract (MOSE) was used in the coagulation process with ferric sulphate and aluminium sulphate (alum) (David et al. 2016). Due to its low cost, availability, and simplicity of handling, alum has been widely used in water and wastewater (Hussaini Jagaba 2018). This study selected alum, ferric sulphate, and copper sulphate for the coagulation process to determine the COD reduction and decolorization efficiency of vinasse treatment.
Biological methods are applied to utilize pollutants for microorganisms’ growth and convert the organic compounds into simpler substances through anaerobic and aerobic processes (Fito et al. 2019). Trickling filters, lagoons, and activated sludge are the most common practical conventional biological treatment methods used in industrial wastewater treatment. A biofilm-based technique called sequencing batch biofilm reactor/submerged bed biofilm reactor (SBBR) could efficiently eliminate pollutants from wastewater. (Ismail et al. 2018). A submerged fixed plastic carrier serves as the foundation of the SBBR system and supports associated growing aerobic bacteria (El-Shafai and Zahid 2013). The aerobic bacteria are active at eliminating organic carbon and nitrogen. SBBR is a basic system that quickly promotes the microorganism’s growth. As a result, SBBRs could remove pollutants, enhance biomass content, and prevent sludge generation while taking up minimal area, being cost-effective, simple to operate and maintain, and decreasing smell and noise (Gómez-Villalba et al. 2006).
Sometimes, a single method is not sufficient for complete distillery wastewater treatment. When the distillery wastewater is partially treated due to the bio-recalcitrant compounds, the dark-brown effluent leaves a foul-smelling with a high COD concentration. Researchers are thus paying close attention to investigate the combined processes of physico-chemical and biological treatments (Oller et al. 2011). The combination of physico-chemical and biological methods included the combination of chemical coagulation, biodegradation, and photo-Fenton oxidation (Rodrigues et al. 2017), the combined biological-electrochemical oxidation treatment (Vilar et al. 2018), and the aerobic fungal growth followed by ozonation (Reis et al. 2019). The combined treatment showed their capability to simultaneously degrade/reduce the pollutants in terms of COD and colour concentrations. The management of distillery effluent using physico-chemical and biological methods together is sustainable and beneficial to the environment by adding value-added products (Ratna et al. 2021).
The focus of the study is to compare the efficiency of three different treatment strategies: coagulation process, SBBR, and combined process of coagulation process and SBBR to produce effluent that complies with discharge standards and allows for water recycling. First, the coagulation process was carried out to examine the effects of various coagulants, initial pH, coagulant dosages, and initial COD concentration in the treatment of vinasse. Next, the effect of the substrate loading concentration was evaluated using SBBR in COD reduction and decolorization. The effect of the substrate loading concentration on the SBBR treatment performance was further analyzed using the kinetic models, ultraviolet-visible spectrophotometry (UV–Vis), and analysis of variance (ANOVA). Then, the effluents of the coagulation process and SBBR were subjected to the following treatment process as the combined sequential treatment process to determine the effectiveness of the combined technologies.