M. Devendran Manogaran

Research background. The rapid growth of the Malaysian population has led to an increase in kitchen waste, especially inedible organic kitchen waste, which is generally disposed of in landfills and pollutes the environment. Apart from this, the increasing demand for chicken products in Malaysia has led to a significant increase in chicken manure production. As anaerobic digestion continues to be explored, there are concerns about the utilization of the digestate from chicken manure. Therefore, this study addresses the challenge of treating kitchen waste and chicken manure digestate in Malaysia by investigating the effectiveness of composting and vermicomposting methods through comparative analysis. By integrating kitchen waste, particularly spent coffee grounds, bone waste and used kitchen towels, this study aims to improve the imbalanced physicochemical properties of digestate from chicken manure. Experimental approach. Before composting, the kitchen waste and chicken manure digestate were characterised to determine the initial physicochemical properties. Four composting setups comprising the substances were established to study the physical appearance, temperature and pH profile, the increase in nitrogen, phosphorus and potassium content, and the mass reduction of the final compost after 50 days of composting. Results and conclusions. The vermicompost with kitchen waste additives showed a significant nutrient improvement with an NPK mass ratio of 1:3.57:6.58 and a lower moisture mass fraction of 48.92 %, which requires the shortest maturation time (20 days) and the highest mass reduction (55.11 %). Novelty and scientific contribution. The novelty of this research is the valorisation of organic kitchen waste and chicken manure digestate as biofertiliser. The end result is achieved by promoting a sustainable alternative to exploit kitchen waste instead of the traditional approach of landfilling waste. At the same time the problem of digestate is addressed, particularly its unbalanced physicochemical properties, especially its macronutrients, pH and moisture content. In contrast to previous studies, this work investigates the effectiveness of both conventional composting and vermicomposting with the incorporation of organic kitchen waste, namely spent coffee grounds, bone meal and used kitchen towels, to improve the physicochemical properties of digestate.

The rapid growth of the Malaysian poultry and palm oil industries has led biomass waste generation in abundance specifically chicken manure and empty fruit bunch (EFB). Anaerobic digestion (AD) is a circular economy-based approach which converts chicken manure and EFB into biogas which can be utilized for heating and power generation. Operating temperature is an imperative consideration for AD hence the objective of the study is to evaluate the effect of different temperature profiles namely, psychrophilic (20 °C), mesophilic (35 °C) and thermophilic (50 °C) on AD of chicken manure and EFB. The kinetic parameters are also evaluated using five kinetic models to enable readers to comprehend the kinetic behaviours of the systems. The volume and composition of biogas is measured every five days for a 50-day retention time. The findings observed that mesophilic condition is the most favourable with cumulative methane, CH₄ composition of up to 17.07%, almost two folds that of thermophilic (9.12%) and five folds that of psychrophilic (3.49%). The CH₄ generation rate, R_b based on the modified Gompertz model which is deemed the best fit further supports these findings as the R_b under mesophilic condition is significantly higher (0.330 mL/g_vs day) compared to psychrophilic (0.088 mL/g_vs day) and thermophilic (0.120 mL/g_vs day) conditions.

Production of 1,2-propanediol and 1,3-propanediol are identified as methods to reduce glycerol oversupply. Hence, glycerol hydrogenolysis is identified as a thermochemical conversion substitute; however, it requires an expensive, high-pressure pure hydrogen supply. Studies have been performed on other potential thermochemical conversion processes whereby aqueous phase reforming has been identified as an excellent substitute for the conversion process due to its low temperature requirement and high H₂ yields, factors which permit the process of in-situ glycerol hydrogenolysis which requires no external H₂ supply. Hence, this manuscript emphasizes delving into the possibilities of this concept to produce 1,2-propanediol and 1,3-propanediol without “breaking the bank” with expenses. Various heterogenous catalysts of aqueous phase reforming (APR) and glycerol hydrogenolysis were identified, whereby the combination of a noble metal, support, and dopant with a good amount of Brønsted acid sites are identified as the key factors to ensure a high yield of 1,3-propanediol. However, for 1,2-propanediol, a Cu-based catalyst with decent basic support is observed to be the key for good yield and selectivity of product. The findings have shown that it is possible to produce high yields of both 1,2-propanediol and 1,3-propanediol via aqueous phase reforming, specifically 1,2-propanediol, for which some of the findings achieve better selectivity compared to direct glycerol hydrogenolysis to 1,2-propanediol. This is not the case for 1,3-propanediol, for which further studies need to be conducted to evaluate its feasibility.