S. A. Ramjani

The pulp and paperboard industries are the major industrial sector that consumes significant amounts of fresh water and generates large volumes of wastewater. The treatment of this wastewater resulted in the production of a substantial amount of sludge, which posed serious environmental challenges. This study explored a sustainable solution by converting PBS into biochar through slow pyrolysis of temperatures up to ≤ 500 °C, offering an alternative approach to waste management and resource conservation. The physicochemical parameters of paper board sludge biochar (PBSB) exhibited a neutral pH of 7.49, electrical conductivity of 0.09 dS m⁻¹, organic carbon of 38.12% and CaCO₃ of 24.5%. Proximate analysis of PBSB revealed an increased fixed carbon of 76.43%, total organic carbon (TOC) of 7.13%, and reduced volatile matter and moisture levels. The TGA analysis of the dried paperboard sludge sample showed a 20% mass reduction when heated to 350 °C. During this process, more than 90% of the volatile components were removed.. The micro nutrients viz., Fe 5.06 mg L⁻¹, Mn 419.3 mg L⁻¹, Cu 26.3 mg L⁻¹, and Zn 66.1 mg L⁻¹ contents were observed in PBSB. FT-IR analysis identified the presence of various carbon-containing functional groups, including C–Cl, C–N, C–C, H–C = O, C–H, and –C≡C–H, indicating substantial chemical transformations during pyrolysis. SEM–EDX analysis revealed that PBSB has fine particle size and a coarse fluffy spongy porous structure ideal for water adsorption. Elemental analysis (XRD) showed high carbon and oxygen content with significant amounts of aluminosilicates, carbonates, and nutrients like phosphorus and potassium, suggesting PBSB as a potential slow-release fertilizer. This research highlights the potential of biochar derived from paperboard waste as a sustainable solution for waste management and resource recovery. Graphical Abstract

Coconut oil production is the eminent agro based industries in Tamil Nadu. The matured coconut water was considered as a waste. Coconut oil industries discharge considerable amount of waste coconut water having very high values of Biochemical Oxygen Demand (BOD) to the extent of 29,000 mgl-1, the wash water about 3,000 mg. and Total Solids (TS) of 5.45 ± 0.35%. Coconut water contains most nutrients required for microbial growth. The pH of coconut water is 6.1. The Total Suspended Solids in coconut water is found out as 0.0028 g/ml. The Total Dissolved Solids is 0.8014 g/ml, Total Solids is 0.8042 g/ml and Volatile Soluble Solids is 99.5 %. A laboratory scale batch type anaerobic digester (Air tight 2 litre plastic bottles) was set up for the experimental purpose for a retention time of 35 days. Coconut water, water and cow dung were mixed in different proportions (5 treatments). Each treatment was replicated 3 times. Biogas volume and biogas composition were measured at 5:30 pm every day. Remarkable volume of biogas production was noticed between 12th and 16th days. Maximum biogas volume of 976. 67 ml was noticed for the combination of 1:1 (Cow dung: Coconut water) with methane content of 53 %. For the combination of 2:1:1 (Cow dung: Coconut water: Water) the maximum volume of biogas production is 833.3ml with methane content of 31 %. For the combination of 1:1 (water: Cow Dung) the maximum volume of biogas produced is 133.3 ml with methane content of 48 %. The biogas produced from different ratios was tested for its flammability. It was seen that blue flame is produced and the flame is last for few seconds for all ratios but the maximum amount of flame was produced from the sample which contains maximum amount of Coconut water than other samples.