Study on development of a device for assessment compost stability based on the determination of oxygen consumption using pressure measurement

Organic fertilizer or compost is an essential product in the current trend of high-tech agricultural development. Compost stability is not only an important quality parameter but can also be used to monitor the efficiency of the composting process. This study developed a device to evaluate the stability of compost based on the oxygen consumption method using the principle of pressure measurement. This homemade device has improved design, overcoming existing weaknesses in commercial equipment with the same operating principle. In which, the compost sample is put in the containers placed in the middle of the bottle while the produced CO2 is absorbed by the KOH solution at the bottom. The device is capable of working independently with the data recorded on the microSD card without connecting to a computer. The device is operationally tested in the laboratory to assess the oxygen consumption of two actual compost samples. The results showed that these samples both meet the EU’s regulations on compost stability with oxygen consumption in 4 days (AT4) less than 10.0 mg O2/g compost.

Compost stability, phytotoxicity and nutrient quality as influenced by carbon to nitrogen ratios of feedstock

Effects of three C/N mixes of groundnut husk (GNH) and Wister rat litter (RL) on stability, nutrient quality and phytotoxicity of compost were tested and compared with the conventional carbon and nitrogen feedstock mix on 1:3 w/w modality respectively. The GNH and RL were respectively composted in a windrow at three proportionate levels (14.7+105.3, 39.2+80.8 and 63.7+56.3 kg) to achieve C/N nutrient ratios of 20:1, 30:1 and 40:1 respectively using the Pearson square method. A control pile containing GNH+RL (tagged conv. 1:3) applied at 30 kg GNH and 90 kg RL using the conventional 1:3 w/w modality was compared in triplicate. Data were taken on daily compost temperature, pH, EC and nutrient content of stabilized composts. Phytotoxicity was assessed by using two compost extract concentrations of 100 and 50% per compost. There were three replications laid in CRD. Data were statistically analyzed. Number of days to compost stability was significantly influenced by C/N with values increasing with decreasing C/N in the order of 59 < 69 < 74 < 77 days for 40:1, 30:1, 20:1 and conv. 1:3 respectively. Increasing C/N decreased pH (range of 7.3 – 9.0), EC (range of 1.2 – 2.7dS/m), ash (range of 44.2 – 55.5%), total macronutrient (N+P+K) (range of 3.56 – 5.15%) and calcium content (range of 3.3 – 6.5%) and increased organic C (range of 22.4 – 29.6%) of the resultant composts and GI (range of 25 – 76%) of cowpea. The 100 and 50% concentrations supported higher GI of cowpea in composts produced from lower and higher C/N respectively.

Composting Hydrochar-OFMSW Digestate Mixtures: Design of Bioreactors and Preliminary Experimental Results

An increasing number of industrial plants integrate the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) with a subsequent composting phase. To improve the plant productivity, a fraction of OFMSW digestate can be converted into a carbonaceous material, called hydrocar (HC), through Hydrothermal Carbonization (HTC), and then composted together with the OFMSW digestate itself, to produce “hydrochar co-compost”. The aim of this paper is to present the design and assembly of batch bioreactors, built in-house to investigate the co-composting process of OFMSW digestate and its HC, and to provide some preliminary results. The OFMSW digestate from an industrial plant was carbonized at 200 °C for 3 h in a 2 L HTC reactor, to produce wet HC after filtration. The ratio of OFMSW digestate and green waste (1:1) used as bulking medium was reproduced in four bioreactors with an increasing percentage of HC substituting the OFMSW digestate (0, 25, 50, 75%). The bioreactors managed to effectively compost the solid wet biomasses in a wet environment with temperature and oxygen control, while measuring online the oxygen consumption and thus the dynamic respirometric index (DRI). The DRI24,max measured with AIR-nl solid respirometer (standardized offline measurement) started from values above 800 mg O2 kgVS−1 h−1 before composting and dropped at the end of the process to values in the range 124–340 mg O2 kgVS−1 h−1 for the four mixes, well below the recommended limit of 500 mg O2 kgVS−1 h−1 for high-quality compost stability. These offline DRI values were confirmed by the online DRI measurements. This research is part of the international C2Land Project funded by the European Institute of Innovation and Technology Climate Knowledge and Innovation Community (EIT Climate-KIC), which is greatly acknowledged.

Lignite Improved the Quality of Composted Manure and Mitigated Emissions of Ammonia and Greenhouse Gases during Forced Aeration Composting

Lignite amendment of livestock manure is considered a viable ammonia (NH3) emission mitigation technique. However, its impact on the subsequent composting of the manure has not been well studied. This work compared changes in biochemical parameters (e.g., organic matter loss and nitrogen (N) transformation) and also the emissions of NH3 and greenhouse gases (GHGs) between lignite-amended and unamended cattle manure during forced aeration composting. Amending manure with lignite did not alter the time to compost stability despite delaying the onset of the thermophilic temperatures. Lignite treatments retained N in the manure by suppressing NH3 loss by 35–54%, resulting in lignite-amended manure composts having 10–19% more total N than the unamended compost. Relative to manure only, lignites reduced GHG emissions over the composting period: nitrous oxide (N2O) (58–72%), carbon dioxide (CO2) (12–23%) and methane (CH4) (52–59%). Low levels of CH4 and N2O emissions were observed and this was attributed to the continuous forced aeration system used in the composting. Lignite addition also improved the germination index of the final compost: 90–113% compared to 71% for manure only. These findings suggest that lignite amendment of manure has the potential to improve the quality of the final compost whilst mitigating the environmental release of NH3 and GHGs.

Deinking sludge compost stability and maturity assessment using Fourier transform infrared spectroscopy and thermal analysis

Thermal composting is an important and useful way to transfer raw organic matter into value-added product rich in humic substances. Furthermore, thermal composting is a very promising way to reduce deinking paper sludge pollutions, which are difficult to remove. The objective of this study was to investigate the behaviour of the composting process of deinking paper sludge with poultry manure over 14 months. Two composts were used: C1 (70/30: deinking paper sludge/poultry manure) and C2 (50/50: deinking paper sludge/poultry manure). The compost stability and maturity were assessed via physico–chemical and thermal analyses: thermogravimetric analysis, differential thermal analysis and diffuse reflectance infrared Fourier transform spectroscopy. Diffuse reflectance infrared Fourier transform spectroscopy analysis provided chemical information for the presence of aromatic, phenolic, aliphatic and polysaccharidic structures. Thermogravimetry analyses revealed that both deinking paper sludge composts were rich in humic acids. The ratio E4/E6 (fulvic acids/humic acids) was also carried out to characterise the maturity index of composts. After 14 months, the compost C2 is more stable, mature and rich in humic acids than compost C1. Furthermore, the addition of poultry manure to the deinking paper sludge-based composts enhanced the formation of humic substances. From 0 to 14 months of composting, the concentration of polychlorinated biphenyls decreased from 0.2 to 0.1 mg kg−1 and from 0.6 to 0.2 mg kg−1 for C1 and C2, respectively.

Assessment of Compost Maturity using The Static Respirometry Index

To be used as organic fertilizer, compost must be stable and mature enough to ensure that it is safe for agricultural application. The stability and maturity of compost can be viewed from physical, chemical, and biological parameters. One of the biological parameters is the static respiration index (SRI). In many places, the SRI is applied as a representative indicator of the stability and maturity of compost but not in Indonesia compost standard of the SNI 19-7030-2004. This study aims to assess the index of the static respiration of composts and analyze their stability and maturity. The assessment was carried out on 10 compost samples sold in Jakarta and Depok. It is observed that 8 of 10 tested composts was stable and mature, with a static respiration index of 0.61–1.35 mg O2 g-1 VS h-1. One of the 10 composts was very stable and very mature, with a static respiration index of 0.46 mg O2 g-1 VS h-1 and 1 compost was unstable and immature, with an index of 1.79 mg O2 g-1 VS h-1. The results indicated that re-composted for seven days was adequate to make the compost more stable and mature than the initial state. Since maturity is not described by a single property, it is great assurance for the compost producer and end user in Indonesia that not only physical and chemical characteristics are used as indicator for compost stability and maturity but also biological indicator such as SRI. Keywords: compost; maturity; stability; static respiration index