The effect of chemical and biological treatments on compost maturity

Introduction:

 In Khuzestan province, Iran, huge amounts of organic waste is generated annually, leading to challenges for its safe disposal, with the waste being usually either burned or land filled.Agro-industrial wastes such as sugarcane pith, have been recognized as important renewable sources of value-added organic products such as compost.Compost is a mixture of decayed organic material decomposed by microorganisms in a warm, moist, and aerobic environment that release nutrients into readily available forms for plant use. Recycling of organic wastes by the process of composting in agriculture brings in the much needed organic matter to the soils and improves the overall soil fertility and soil productivity Thus, composting is a process for appropriate disposal of waste and is also beneficial from ecological and economic point of view. Lignocellulosic materials are not easily degraded due to the lignin, crystalline and structural complexity of cellulose matrix. Application of chemical and biological treatments may increases waste degradation and decrease composting process time. Bacteria and fungi are the two main microbes that help in decomposition of organic waste and forces of composting. In addition, efficient composting is dependent on the microbial activity. The objective of this research was to investigate the effect of chemical (gypsum) and microbial treatments (consortium of bacteria and fungi) on reduce C/N and shortening process of compost maturity which is used in agricultural fields. 

Materials and Methods:

 In this research, an incubation experiment was carried out in laboratory condition as a factorial experiment based on a randomized complete design with two factors: 1) gypsum application in three levels including, 1%, 5% and 10% w/w, and 2) microbial inoculation in four levels including control (without microbial inoculation), inoculation of substrate with consortium of bacteria, consortium of fungi and consortium of bacteria + fungi, with three replications. The sugarcane pith for compost production was collected from Dehkhoda sugarcane Agro-industry, Ahvaz, SW Iran. The sugarcane pith was initially boiled for 2h, then air-dried. Sugarcane pith samples were sterilized in an autoclave and 1% w/w urea were added to each samples to reduce their C/N ratio. Then, sterilized gypsum and microbial treatments were added to samples in plastic jars. Samples were incubated for 90 days at constant temperature of 25 ± 2 °C. Samples moisture content was maintained at 80% of field capacity. The samples were weighted every day and the required amounts of distilled water were added. At the end of incubation period, sample properties such as organic matters loss percent (OM loss), ash content, carbon (C), nitrogen (N), hydrogen (H) and sulfur (S) content were measured. Also oxygen (O) content and atomic ratio including carbon to nitrogen (C/N), hydrogen to carbon (H/C), oxygen to carbon (O/C) and hydrogen to oxygen (H/O) ratio were determined. All statistical analyses were performed using SAS software. Means of different treatments were compared using the Duncan’s test at probability level of 5%. 

Results and Discussion:

 The results of variance analysis showed that the gypsum levels and microbial treatments significantly affected the organic matters loss percent, carbon, nitrogen, hydrogen and sulfur content and O/C, H/O and H/O ratio. In addition interaction effect of gypsum and microbial treatments was significant on nitrogen, hydrogen content and C/N ratio. The results indicated that the gypsum addition and inoculation of bacteria and fungi consortium to sugarcane pith significantly (P < 0.05) decreased the carbon content and C/N, H/C and H/O ratio, while significantly (P < 0.05) increased nitrogen, oxygen and hydrogen content as well as O/C ratio. With increasing gypsum levels (from 1 to 10% w/w) the carbon content and C/N, H/C and H/O ratio significantly (P < 0.05) reduced, while nitrogen, oxygen and organic matter loss percent, hydrogen content and O/C ratio significantly (P < 0.05) increased. Comparison of microbial treatments showed that consortium of bacteria + fungi had higher effect on changes in organic matter loss percent, carbon and nitrogen content and C/N, H/C, H/O and O/C ratio. Maximum organic matter lost and nitrogen content as well as minimum and C/N, H/C and H/O ratio were recorded for co-inoculation of bacterial and fungi consortium combined with application of 10% gypsum treatments. Reduction of C/N, H/O and H/C as well as increasing O/C in the above mentioned treatment, indicating that maturation of sugarcane peat composting was completed three months after composting process.

Conclusion:

 From the results of this study, it can be concluded that inoculation of consortium of bacteria and fungi with 10% gypsum led to hasten the sugarcane pith degradation and shortening composting process duration.