Plant herbs specifically serai wangi (SW) and peppermint (PPM) are selected for its insect repellent properties as the use of chicken manure (CM) in anaerobic digestion (AD) potentially attract flies due to the digestate produced. Hence, the addition of SW and PPM in the AD system of CM could deter flies' infestation while producing biogas. Previous work has shown that AD of sawdust (SD) and CM with these plant herbs were able to produce biogas and reduce the flies attraction towards the digestate. However, the combination of SW and PPM for AD of CM has yet to be investigated. This work describes the effect of mixing SW and PPM on the co-AD of SDCM with respect to biogas production, methane yield and kinetic analysis. The mixture of SW and PPM was varied at different concentrations. The composition of methane in biogas was characterized every 10 days by using gas chromatography (GC) equipped with a thermal conductivity detector (TCD). The results suggest that co-AD of 10SW10PPM exhibited the highest biogas production (52.28 mL/g_vs) and methane yield (30.89 mL/g_vs), which the purity of methane increased by 18.52% as compared to SDCM. However, increasing the concentration of SW and PPM does not significantly improve the overall process. High R² (0.927-0.999), low RMSE (0.08-0.61) and low prediction error (<10.00%) were displayed by the modified Gompertz, logistic and Cone models. In contrast, Monod and Fitzhugh model is not preferred for the co-AD of SDCM with a mixture of SW and PM, as a high prediction error is obtained throughout the study. Increasing the dosage of PPM decreases the maximum cumulative methane yield, ranging from 31.76 to 7.01 mL/g_vs for modified Gompertz and 89.56 to 19.31 mL/g_vs for logistic model. The Modified Gompertz obtained a lag phase of 10.01-28.28 days while the logistic model obtained a lag phase of 37.29-52.48 days.

The gas sweetening process removes hydrogen sulfide (H₂S) in an acid gas removal unit (AGRU) to meet the gas sales’ specification, known as sweet gas. Monitoring the concentration of H₂S in sweet gas is crucial to avoid operational and environmental issues. This study shows the capability of artificial neural networks (ANN) to predict the concentration of H₂S in sweet gas. The concentration of N-methyldiethanolamine (MDEA) and Piperazine (PZ), temperature and pressure as inputs, and the concentration of H₂S in sweet gas as outputs have been used to create the ANN network. Two distinct backpropagation techniques with various transfer functions and numbers of neurons were used to train the ANN models. Multiple linear regression (MLR) was used to compare the outcomes of the ANN models. The models’ performance was assessed using the mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R²). The findings demonstrate that ANN trained by the Levenberg–Marquardt technique, equipped with a logistic sigmoid (logsig) transfer function with three neurons achieved the highest R² (0.966) and the lowest MAE (0.066) and RMSE (0.122) values. The findings suggested that ANN can be a reliable and accurate prediction method in predicting the concentration of H₂S in sweet gas.

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.

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.