Nowadays, composting is the method of choice to reduce and recycle the ever increasing organic wastes generated from human activities. The four phases of composting and the factors affecting each phase, particularly carbon to nitrogen ratio, temperature, aeration, moisture content and pH are critically reviewed. The process of composting is believed dependent on the microbial activities such as bacteria, fungi and actinomycetes under the stipulated conditions. The inoculation of beneficial microbes in the compost would further enhance the soil fertility and crop productivity. However, the interaction between the species of microorganisms is still unknown. Organic matters are composted into humid substances which can be used for the promotion of sustainable agriculture. In addition to plant growth promotion, microbiological additives inoculated compost is also likely to increase plant stress tolerance and disease suppression capacity. The completion of decomposition is usually measured based on the physical appearance of compost, the chemical property of compost substances, as well as the absence of toxins, noxious odor and pathogenic microbes. The application ofmature compost is of great importance because direct application of organic matters into the soil may produce toxins and threaten the ecosystem.
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.
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.
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.
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.
Organic waste valorisation processes becoming popular organic waste management strategies in recent years, as resolving the environmental issues caused by organic waste disposal and making it into useful resources. Organic wastes can be valorised by mixing with other organic wastes to fulfil the requirement of designated bioprocesses such as the production of H2, CH4 and C2H5OH. The amount of carbon and nitrogen was the main factor to be considered in this study, expressed in terms of carbon-to-nitrogen ratio number, NC:N. The locally available organic wastes were used as the main supply of carbon and nitrogen. As the organic waste produced in different cities varies every day, the local organic wastes might not be able to provide sufficient carbon and nitrogen demanded by the designated bioprocesses. This research will reveal the amount of carbon and nitrogen required from external supplies to mix with the carbon and nitrogen found in local organic wastes. This research developed an Organic Waste Valorisation Pinch Analysis (OWVPA) in terms of carbon-to-nitrogen ratio numbers combined with reversed SCC shifting approaches. This Pinch Analysis is a robust and effective tool to estimate the mass flowrate and carbon-to-nitrogen ratio numbers of external supplies required by the designated demand sides.
'/%3e%3cuse xlink:href='%23a' transform='translate(0 -400)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -600)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -800)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1000)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1200)'/%3e%3cpath d='M0 0h1400v800H0z' style='fill:%23010066'/%3e%3cpath d='M576 100c-166.146 0-301 134.406-301 300s134.854 300 301 300c60.027 0 115.955-17.564 162.927-47.783-27.353 9.44-56.71 14.602-87.271 14.602-147.327 0-266.897-119.172-266.897-266.01 0-146.837 119.57-266.01 266.897-266.01 32.558 0 63.746 5.815 92.602 16.468C696.217 118.91 638.305 100 576 100z' style='fill:%23fc0'/%3e%3cpath d='m914.286 471.429-99.538-53.25 29.43 108.982-66.575-91.165-20.77 110.96-20.428-111.024-66.857 90.96L699.314 418l-99.701 52.943 74.065-85.192-112.8 4.441 103.694-44.62-103.555-44.94L673.8 305.42 600 220l99.538 53.25-29.43-108.982 66.575 91.165 20.77-110.96 20.428 111.023 66.857-90.959L814.97 273.43l99.702-52.944-74.065 85.193 112.8-4.441-103.694 44.62 103.555 44.94-112.785-4.79z' style='fill:%23fc0' transform='matrix(1.2738 0 0 1.2423 -89.443 -29.478)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='translate(288.889 -214.211)'/%3e%3cuse xlink:href='%23a' transform='translate(108 342.749)'/%3e%3cuse xlink:href='%23a' transform='translate(469.189 342.749)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)