Review on the characteristic and feasibility of leachate for biogas production by anaerobic digestion

The sound handling of municipal solid waste (MSW) is of high priority to minimise environmental degradation and pollution. MSW can be treated via various technologies including landfilling, incineration, composting, anaerobic digestion (AD) and more. Landfill without landfill gas capturing serves as an enclosed bioreactor to store and stabilise waste. Other technologies such as incineration, composting and AD allow substantial volume reduction and generate value-added products. The treatment for MSW is commonly focusing on the solid part. Organic waste contains high moisture content of 70 - 90 %. The pressing of the water content before entering treatment unit, the release of water during and after the treatment, can generate high strength wastewater, known as leachate. Leachate is rich in organic matter, organic pollutants, pathogens, heavy metals and more, which can lead to severe secondary environmental pollution if not properly treated. Leachate from different treatment units showed certain unique characteristics, such as high Na, high Ca, different species and availability of heavy metals. This review summarised some of the important characteristics of different leachates and the suitability of AD as a mean of treatment. The efficiency of AD to treat leachate was presented in terms of the removal efficiency of chemical oxygen demand (COD) and biogas production. The COD removal efficiency was between 60 - 98 %, following the treatment of different leachates under different reactors and operational parameters. Among the different stream of leachates, the leachate from landfill is most commonly studied as a co-digestion substrate for AD, as compared to leachate from the composting facility

Effective microorganisms on organic matter with carbon and nitrogen mineralisation for empty fruit bunches composting

This project aims to investigate the effect of Effective Microorganisms (EM) on the composting of oil palm empty fruit bunch (EFB) through organic matter degradation with carbon (C) and nitrogen (N) mineralisation by comparing the control sample (CTL) of EFB with no EM treatment and the EM-treated EFB sample (ETC). The maximum C mineralisation for CTL and ETC was recorded as 671.4 ± 86.55 mg CO2 Ckg-1d-1 on day one and 713.5 ± 68.5mg CO2 Ckg-1d-1 on day two respectively. ETC had C mineralisation remained significantly higher than CTL from day 28 until day 40 before falling on day 41 and became on par with CTL. The total organic matter loss was 3.75 ± 1.35% for CTL and 10.78 ± 3.77% for ETC. This resulted in a total mineralised C of 32.97 ± 2.25% and 37.7 ± 2.53% total organic carbon for CTL and ETC, respectively. For N mineralisation, the presence of NH4 + in early stage followed by NO3 - dominance on later stage indicated successful composting. CTL had final value of 0.1 and ETC had 0.04 for NH4 +/NO3 - ratio. For curve fitting, first order kinetic model and first order exponential model were chosen as they were showed to better describe mineralization for recalcitrant organic matter by other studies. The first order exponential model showed better fit with p-value of 0.275 as compared to the first order model with p-value of 0.981 in this work. First order kineitc model failed to describe the N mineralisation with a high p-value of 0.989. The unfitness of models could be due to insufficient data over limited experimental time and sampling error for heterogenous materials. This study showed that both CTL and ETC were able to produce mature compost but ETC had better performance on the efficiency of EFB composting based on organic matter degradation, C and N mineralisation coupled with several others parameters (C/N, temperature, pH and microbial profile)

A review on the impacts of compost on soil nitrogen dynamics

With the depletion of soil quality, the increased use of inorganic fertiliser is required to cope with the increasing food demand. The increasing use of inorganic fertiliser has become a burden to both the economy and environment. The overuse of nitrogen fertiliser can cause the leaching of NO3- to the surrounding water source and the emissions of N2O and NO to the atmosphere. Besides the environmental issues associated with conventional farming, more attention has been drawn to the rapid population growth and urbanisation that has led to the production of abundant municipal solid waste (MSW). To overcome these problems, composting can be an alternative option to both managing MSW and replacing inorganic fertiliser. As a biological process, composting can utilise the organic fraction of MSW as the raw material to produce compost, a stable form of organic matter that can be used as soil amendment or organic fertiliser. Although the utilisation of compost as an organic fertiliser is quite well studied, less research had focused on the nitrogen dynamic after compost application to soil. It is essential to figure out the correlation between compost application and soil nitrogen dynamic in order to prevent further nitrogen loss as a pollutant after compost application. This paper reviews the soil nitrogen cycle and the potential of nitrogen loss prevention with the application of compost. The application of compost is providing some promising effects in term of soil organic carbon and nutrients replenishment and soil microbial population enhancement. The effects of compost to soil are highly dependent on the characteristics of the raw materials for composting. The presence of high nutrient in compost is not always a good thing since it also increases the risk of nutrient loss through leaching or gas emission. The combination between nutrient rich and nutrient poor compost can be an alternative way to prevent nutrient loss. N2O emission from soil is always associated with high nitrogen content and anaerobic condition in soil. The mitigation of N2O emission can be achieved by compost application, and the addition of biochar during composting process can further enhance the effect

Environmental and economic feasibility of an integrated community composting plant and organic farm in Malaysia

Waste prevention and management become a significant issue worldwide to achieve sustainable development. Similar to many developing countries, Malaysia has faced severe problems in waste management due to its rapid economic growth and urbanisation. The municipal solid waste (MSW)production rate in Malaysia had increased significantly in a recent year, ranging from 0.8 to 1.25 kg/person∙d. The wastes generated contain a high amount of organic portion with high moisture content. Improper MSW management practice or delayed in waste collection and transportation can lead to severe health issues. This paper presents a case study in Johor Bahru, Malaysia (FOLO Farm), in which a composting prototype is used as the waste management technology to recycle the food and vegetable wastes. The greenhouse gases (GHG)mitigation and economic feasibility of the integrated composting and organic farming in this study are reported. This study showed a reduction of 27% of GHG by diverting the food and vegetable wastes from open dumping to the composting plant. Higher reduction rate (∼44%)can be achieved with better planning of waste collection route and applying the mitigation strategies during the composting process. By adapting the membership concept, this project not only ensures the economic feasibility of running a composting plant but also secures a channel for the growth of vegetable distribution. This study provides an insight into the feasibility and desirability to implement a pilot-scale composting for organic waste management to achieve the low carbon and self-sustain community

The characterisation and treatment of food waste for improvement of biogas production during anaerobic digestion - A review

Anaerobic digestion is one of the major biological-based technologies for converting organic waste to energy. The end-product of the process is the production of biogas that can be harvested as renewable energy and a nutrient-rich digestate that can be transformed as biofertiliser. Food waste varies seasonally and geographically, leading to a variation of biogas potential among different studies. There is still a lack of study on the relationship among the variation of food waste characteristic, its effect on the operational parameters and their inhibition value and its effect on the efficiency of the methods for improving biogas production. This paper reviews the anaerobic digestion of food waste in three sections: the characteristic of food waste reported in the literature, mono-digestion of food waste and co-digestion of food waste with other feedstocks. This review aims to relate the characteristics of food waste to biogas potential and to propose process improvement for enhanced biogas production. Food waste showed variation in terms of bromatological analysis, where the carbohydrates was reported to be around 11.8–74%, protein was 13.8–18.1% and lipid was 3.78–33.72%. The biogas yield for mono-digestion of food waste was 0.27–0.642 m3 CH4/kg VS and for the co-digestion of food waste with other substrates was 0.272–0.859 m3 CH4/kg VS. It has been concluded that the variation in the characteristic of food waste, in terms of physical and biochemical properties, can affect the efficiency of the applied treatment for process improvement, including nutrient balance, mechanical treatment, thermal treatment and two-stage configuration. Co-digestion remains an effective method for biogas production from food waste. Thermal treatment can significantly increase biogas production but excessive treatment can reduce the biodegradability of food waste. Mechanical treatment is more effective in treating waste rich in cellulosic material

Selection of parameters for soil quality following compost application: A ranking method

Intensive agricultural practices with excessive use of chemical fertiliser have led to the deterioration of soil fertility where soil losses its ability to sustain a consistent crop system with high yield. Compost is a potential substitution to chemical fertiliser. As a biological additive, compost can improve soil quality and crop productivity, controlling plant diseases and reduce nutrient loss and water pollution. However, the effect of compost application to enhance the quality of the soil may be inconsistent due to the slow release nature of the nutrients, compost quality, types of feedstocks and other factors. To evaluate the effects of compost application, it may involve a large number of parameter analyses, which can be costly and time ineffective. There is no indicator to reduce the number of analyses concerning the effect of compost application on soil fertility. In this study, a ranking method is proposed to identify the minimum number of parameters able to track the effect of compost application on soil fertility and the environmental impact. A total of 23 soil parameters were selected through literature review and ranked for their importance to show the effect of compost use. The ranking method was developed based on (1) the reporting frequency of environmental and soil fertility parameters and (2) impact of the selective parameter to the environment. Soil C and N contents were found to be the most frequently reported parameters (85 and 90 %) to affect soil fertility upon compost application. Both contents in the soil also change significantly before and after compost application. Heavy metals and N2O emissions were found to impact the environment most due to the toxicity of heavy metal to the environment and human health and high global warming potential of N2O. Based on the ranking method, nine parameters (N, NO3--N, P, K, micro-nutrients, heavy metals, C, pH and N2O emissions) were selected. 60 % of soil analyses were reduced following this ranking method. For the future study, a weightage system could be implemented on each criterion to decide the more essential parameters to be evaluated based on different soil or crop type and under different agricultural practices

Isolate new microalgal strain for biodiesel production and using FTIR spectroscopy for assessment of pollutant removal from Palm Oil Mill Effluent (POME)

In tropical countries, the palm oil industry discharges a large amount of wastewater. The wastewater can serve as an economical nutrient source or substrate that can support the cultivation of microalgae. This study aimed to identify the local species of microalgae potentially existing in the industrial wastewater of palm oil mill effluent (POME). POME was selected as the key source of waste due to its higher potential in producing lipids from microalgae as biofuel substrate. A novel green microalgal strain was isolated from POME of Kahang- Johor west palm oil mill in Malaysia and was identified as Chlamydomonas sp. and subsequently named UTM 98 with Catalogue No. of KR349061. This study emphasised the effectiveness of POME as the main carbon source to maintain the growth of microalgae and simultaneously to increase the lipid content. In this study, Fourier Transform Infrared spectroscopy (FTIR) and Gas Chromatography (GC-FID) were used to identify andquantify lipids in the freshwater microalgae. Cultivation of microalgae were initially carried out in 250 mL Erlenmeyer flask containing 100 mL medium at ± 30 °C with continuous illumination (± 14 µmol-1 m-2 s-1) andup to 20 d of cultivations. Results demonstrated that on the chromatogram, the highest retention achieved is belong to palmitic acid (C16:0). Chlamydomonas incerta (C. incerta) species is found to contain shorter chain fatty acids, mainly 16 - 18 carbon length, which is ideal for biodiesel production. FTIR spectrum of POME treated biomass displayed the shifting of peak at 591 cm-1 and also removal of C-Cl stretching. The spectrum of POME effluent treated biomass revealed broad peak at 3,430 cm-1. The results of SEM micrographs showed that, after treating POME with C. incerta, the cells became slightly rough and corrugated textures and some particles were found on the surface of the cell wall. Using POME as a rich carbon and nutrient source is also a promising approach either as natural environment treatment or as high-lipid-content raw material for production of biofuel

Integrating compost and biochar towards sustainable soil management

Composting of biowaste to organic fertiliser promotes resource recycling with various environmental co-benefits, including mitigation of nutrient loss, greenhouse gas emissions, and soil enrichment. As produced from the pyrolysis of organic waste, biochar could be added to compost for enhanced performances. The use of either compost or biochar or both has shown a positive effect on the overall soil quality, such as increasing soil pH and electrical conductivity, increasing soil organic matter, promoting soil carbon storage, and reducing the bioavailability of heavy metals. However, studies have reported contradictory observations and varying degree on the positive effect of such amendments on the aspects mentioned above. This review aims to evaluate the effect of biochar on composting towards a greener and cleaner process. The interacting mechanisms among biochar, compost and biochar-compost amendment upon soil application are discussed. The addition of biochar to compost effectively reduces nutrient loss and gaseous emission and promotes humification. The presence of biochar enrich specific groups of microbes that encourage nitrogen immobilisation. Biochar is more effective in improving the soil carbon pool, whereas compost has a more direct and persistent impact on the soil pH and cation exchange capacity. Upon applying mixed compost with biochar in soil, the organic amendments reduced heavy metals' bioavailability through the respective mechanisms. Different effects of compost and biochar on the soil properties and microbial community were observed, depending on the amendment type, soil condition and length of the application period

Optimization of solid waste management in rural villages of developing countries

, , , , Optimum municipal solid waste (MSW) management system is an essential aspect to be considered. Optimal MSW management system could incur high cost of investment related to its construction, operation, and maintenance. The optimal configurations of the technologies within the system are of high importance, especially in developing countries due to the limitation on financial support. There are still limited studies on the integration of the possible configurations of the selected MSW management, which are centralized, clustered, and decentralized, in addition to location planning. A cost optimization model with the consideration of location planning is developed to identify the optimal configuration of the MSW management system with technologies considered such as landfilling, composting, refuse derived fuel, and reuse and recycling. The configuration considered in the study includes a centralized system, where all waste is gathered in a specific location and treated. The second configuration is the clustered system, where zones are identified, and waste treatment center is built in each zone. Finally, the decentralized, where smaller treatment centers are built at each village. The case study took place at the Desoq District, Kafr El Sheikh, Egypt. It is inhabited with a population of about 0.5 M capita. Fifteen scenarios are generated to account for the different combination of system configurations and the type of waste treatment and disposal unit. A mixed integer linear programming (MILP) model is developed to perform the optimization. The results showed that increasing in the type and degree of treatment increases the net profit. This means that the incorporation of sorting, recycling, composting and RDF production leads to higher profit compared to landfilling only. The centralized systems turned out to attain more net profit than decentralized and clustered systems. The optimum scenario with maximum net profit value was the centralized system with sorting, composting, waste to energy facilities, and one landfill with a net profit of 3.864 USD/t/d. The optimal location for such centralized system is identified to be located beside Desoq wastewater treatment plant and between Desoq and Sanhour cities. The same model can be applied to other rural areas in developing countries

Mitigation of soil salinity using biochar derived from lignocellulosic biomass

Soil salinisation is recognised as a serious form of soil degradation, affecting crop production and compromising food security. It is crucial to remediate the negative impacts of soil salinisation to improve the associated soil functions. Various organic and inorganic amendments are used for saline soil remediation. Biochar, known as the porous solid carbonaceous material produced at elevated temperatures ranging from 300 °C to 1,000 °C under oxygen deficit condition, is gaining considerable attention. Biochar is widely reported to enhance the sorption of nutrients and reduce nutrient leaching from the soil. Biochar application is effective in improving the physical, chemical and biological properties of saline soil. Limited studies were reported on the role of biochar to mitigate soil salinity, especially in terms of their adsorption mechanisms. This paper review the various role of biochar, derived through the pyrolysis of fibrous biomass, to improve the physical properties (soil porosity, soil aggregation, water holding capacity, hydraulic conductivity and organic carbon content) and chemical properties (pH, electrical conductivity, exchangeable sodium percentage and sodium adsorption ratio) of saline soil. Physical adsorption and ion exchange are found to be the most common remediation mechanisms of saline soil by biochar