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<p>Anaerobic digestion (AD) is a sustainable waste-to-energy technology that addresses both environmental pollution and renewable energy generation. This study investigates the potential use of parboiled rice mill wastewater (PRMWW), assesses the energy balance of its co-digestion process, and addresses water requirements in AD. Since PRMWW has an unbalanced nutrient profile, particularly low in carbon, its co-digestion with lignocellulosic substrates such as rice straw (RS) can enhance overall digestion efficiency by improving the nutrient balance and promoting lignocellulose degradation. RS was incorporated into PRMWW to balance the carbon-to-nitrogen (C/N) ratio and provide structural carbon for enhanced biogas production. Various co-substrate combinations with different C/N ratios were tested under mesophilic conditions. The study investigated the effect of RS particle size on biogas production and observed that medium-sized particles (1.18–2.36&#xa0;mm) yielded higher biogas compared to small (0.6–1.18&#xa0;mm) and large (2.36–4.75&#xa0;mm) particles. The corresponding biogas yields were 363, 439, and 313 mL/g VS<sub>added</sub> for small, medium, and large particles, respectively. Additionally, it was observed that increasing the C/N ratio beyond a certain point reduced biogas production due to nitrogen limitation. At C/<i>N</i> = 23 with RS particles of medium, methane and biogas yields were 235 and 439 mL/gVS<sub>added</sub>, respectively, with an 83% reduction in volatile solids (VS). The impact of the inoculum-to-substrate (I/S) ratio (0.5 to 4) on digester performance was also examined. The optimal I/S = 1 produced significant yields of 443 mL/gVS for biogas and 267 mL/gVS for methane, with 72% biodegradability. The modified gompertz model (MGM) showed the highest methane production (268.59 mL/gVS) after a lag period of 2.60 ± 0.71 days. The energy balance analysis of anaerobic co-digestion (ACoD) of PRMWW and RS reveals a net energy gain of 43.75 kWh/MgVS, demonstrating superior energy yield compared to mono-digestion.</p>

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Synergistic Anaerobic Co-Digestion of Parboiled Rice Mill Wastewater and Rice Straw: Influence of Particle Size and Inoculum-to-Substrate Ratio on Biogas Kinetics and Energy Balance

  • 期刊论文

  • 发表日期：

    2025年11月20日

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  • Nagarjuna Kandagatla,
  • Sridhar Pilli,
  • Polisetty Venkateswara Rao,
  • R. Satish Babu,
  • R. D. Tyagi

摘要

Anaerobic digestion (AD) is a sustainable waste-to-energy technology that addresses both environmental pollution and renewable energy generation. This study investigates the potential use of parboiled rice mill wastewater (PRMWW), assesses the energy balance of its co-digestion process, and addresses water requirements in AD. Since PRMWW has an unbalanced nutrient profile, particularly low in carbon, its co-digestion with lignocellulosic substrates such as rice straw (RS) can enhance overall digestion efficiency by improving the nutrient balance and promoting lignocellulose degradation. RS was incorporated into PRMWW to balance the carbon-to-nitrogen (C/N) ratio and provide structural carbon for enhanced biogas production. Various co-substrate combinations with different C/N ratios were tested under mesophilic conditions. The study investigated the effect of RS particle size on biogas production and observed that medium-sized particles (1.18–2.36 mm) yielded higher biogas compared to small (0.6–1.18 mm) and large (2.36–4.75 mm) particles. The corresponding biogas yields were 363, 439, and 313 mL/g VSadded for small, medium, and large particles, respectively. Additionally, it was observed that increasing the C/N ratio beyond a certain point reduced biogas production due to nitrogen limitation. At C/N = 23 with RS particles of medium, methane and biogas yields were 235 and 439 mL/gVSadded, respectively, with an 83% reduction in volatile solids (VS). The impact of the inoculum-to-substrate (I/S) ratio (0.5 to 4) on digester performance was also examined. The optimal I/S = 1 produced significant yields of 443 mL/gVS for biogas and 267 mL/gVS for methane, with 72% biodegradability. The modified gompertz model (MGM) showed the highest methane production (268.59 mL/gVS) after a lag period of 2.60 ± 0.71 days. The energy balance analysis of anaerobic co-digestion (ACoD) of PRMWW and RS reveals a net energy gain of 43.75 kWh/MgVS, demonstrating superior energy yield compared to mono-digestion.