Sustainable treatment of acidic coffee wastewater using biomaterials

Abstract

Coffee wastewater (CWW), a byproduct of coffee processing industries, is characterized by high acidity and elevated organic loads, including COD (Chemical Oxygen Demand) and BOD5 (five-day Biochemical Oxygen Demand), which pose significant environmental risks to downstream users. Anaerobic biological treatment is widely recommended to reduce these organic pollutants. However, the low carbon-to-nitrogen (C:N) ratio and acidic nature of CWW inhibit methanogenic microbial activity, limiting both biogas production and treatment efficiency. This study addresses these challenges by evaluating two pH neutralization strategies carbonized coffee pulp (CCP) and lime (Ca(OH)2) prior to anaerobic digestion. To assess the impact of each neutralization method, batch anaerobic digesters were operated under mesophilic conditions (37 °C) using 550 mL of pretreated coffee wastewater with a hydraulic retention time of 25 days. CCP and lime were applied at dosages of 1.8 kg/m3 and 3.5 kg/m3, respectively, to raise the initial pH to the optimal range for methanogenesis (7.5). Results demonstrated that CCP treated samples significantly outperformed lime-treated samples. CCP achieved a 90 % reduction in COD (from 10,240 mg/L to 1024 mg/L), an 85 % reduction in BOD5 (from 5000 mg/L to 750 mg/L), and the highest biogas yield of 4000 mL. In comparison, lime-treated samples achieved 50 % COD and 60 % BOD5 removal, with a biogas yield of 1175 mL. The superior performance of CCP is attributed to its high carbon content (C:N ratio of 42.94:1) and its ability to stabilize pH without causing sedimentation or scum formation. In conclusion, CCP is a more effective neutralizing agent for coffee wastewater treatment than lime, offering enhanced biodegradability, improved nutrient balance, and substantially higher biogas production. Its dual role as a pH stabilizer and organic enhancer makes CCP a sustainable and cost-effective alternative to conventional chemical neutralizers in anaerobic digestion systems.