International Journal of Recycling of Organic Waste in Agriculture
Volume:9 Issue: 1, Winter 2020

Purpose Biogas residues, digestates, contain valuable nutrients and are therefore suitable as agricultural fertilizers. However, the application of fertilizers, including digestates, can enhance greenhouse gas (GHG) emissions. In this study different processes and post-treatments of digestates were analyzed with respect to triggered GHG emissions in soil. Methods In an incubation experiment, GHG emissions from two contrasting soils (chernozem and sandy soil) were compared after the application of digestate products sampled from the process chain of a food waste biogas plant: raw substrate, digestate (with and without bentonite addition), digestates after separation of liquid and solid phase and composted solid digestate. In addition, the solid digestate was sampled at another plant. Results The plant, where the solid digestate originated from, and the soil type influenced nitrous oxide (N2O) emissions significantly over the 38-day experiment. Composting lowered N2O emissions after soil application, whereas bentonite addition did not have a significant effect. High peaks of N2O emissions were observed during the first days after application of acidified, liquid fraction of digestate. N2O emissions were strongly correlated to initial ammonium (NH4+) content. Conclusion Fertilization with dewatered digestate (both fractions) increased N2O emission, especially when applied to soils high in nutrients and organic matter.

Purpose Soil salinization is one of the most severe abiotic stresses which threaten sustainable agriculture in arid and semi-arid regions including Morocco. The application of organic amendments like composts to saline soils has been confirmed to alleviate soil salinity stress. The present work aims to study the effect of humic acids (HA), as one of the products resulting from organic matter decomposition, on soil salinity reduction. Methods In this perspective, four composts made from mixtures corresponding to initial C/N ratios of 25, 30, 35 and 40 were tested. The four composts were made from mixtures of different proportions of greenhouse wastes, olive mill waste and sheep manure in Souss-Massa region. Representative samples underwent physicochemical analysis, extraction, purification and analysis of HA. The maturity of compost was assessed through some maturation index, prior to the main trial of the interaction between extracted HA and sodium carbonates salt (Na2CO3), largely encountered in saline soils. Results The results showed that the compost with initial C/N ratio of 35 is the most recommended for application as an amendment to alleviate soil salinity. Conclusion The salt stress alleviating effect of compost may be advocated to compost humic acids and their ability to chelate sodium on their carboxylic sites.

Purpose Food waste can be referred to as edible food materials that can create problems to the environment if it is not disposed properly. Therefore, the purpose of this study is to produce chicken feed from food waste via two-stage fermentation. Methods Food waste was converted with combination of fungi A (isolated from degraded onion) and yeast B (isolated from local fermented fruit - Durian). Four batches of food waste were obtained from different sources. Food waste was fermented with fungi A and yeast B in bioreactor for 5 days with 80% moisture content. Fermented food waste was then dried in the oven. Results Glucose and carbohydrate contents were investigated during fermentation process and it was found that carbohydrate content decreased from 0.1857 g/g before fermentation to 0.1305 g/g after fermentation. Glucose content was found to increase at the first 48 hours and then dropped from 48th hour until the fermentation was done. To get consistent with the results of the last product, the process control elements such as C:N ratio, pH, aeration, agitation, temperature, antiseptic technique and sterilization of food waste were controlled. The standard of the fermented food waste was compared with the standard of chicken feed used in Malaysia. The crude protein content, crude fat content, crude fiber content, total ash content and total energy content of chicken feed met the requirement set by Malaysia standard (MS 20:2008) of chicken feed. Conclusion Thus, it is shown that food waste has a massive potential in the production of chicken feed.

Purpose The effect of using compost and vermicompost or their teas on the growth and biochemical profile of Salvia officinalis cultivated in sand soil were assessed. Methods Plants were subjected to different treatments of compost, vermicompost and their teas. The growth of common sage, Salvia officinalis was monitored as shoot fresh and dry weights (g/plant) and their oil, N, P, and K contents. Results Among the four tested treatments of vermicompost, the treatment no. 1 (prepared from rice straw supplemented by Trichoderma harzianum and Phanerochaete chrysosporium + Cattle dung + Rock phosphate + Feldspar “12 % K2O”), showed the maximal values of shoot fresh and dry weights, oil, N, P, and K %, being in the first cut 820, 200 g/plant, 1.42, 2.80, 1.40 and 1.98 in respective order. The corresponding values in the second cut were 1152, 277 g/plant, 1.55, 3.56, 1.68 and 2.29%, respectively. Also, the maximal values of all previous parameters were recorded in the vermicompost tea treatment no1, treated as soil and foliar amendments being 730, 196 g/plant, 1.47, 2.4, 1.38 and 2.19% in the first cut and 1150, 270 g/plant, 1.64, 3.5, 1.68 and 2.38% in the second cut, respectively. Conclusions The growth of Salvia officinalis was higher in plants treated by different vermicompost treatments, compared to those treated by compost or the control (without any supplementation).

Purpose The uncontrolled discharge of phosphorus into aquatic environment leads to the deterioration of the water bodies. Additionally, the agricultural crops present inside the La Albufera de Valencia Natural Park, rice fields mainly, have a high social and environmental value. However, there is a conflict between private interests (farmers) and public interest in the management of agro-waste produced by them. Nowadays, the option used by the farmers is the uncontrolled burning in the own field. The ashes generated during the combustion process could be used to remove phosphorus loading in water bodies of the Natural Park, contributing to its recovery. Methods Adsorption experiments were carried out in batch mode by using different concentrations (5-100 mgP L-1) of sodium phosphate dibasic (Na2HPO4) placed in 100 mL stoppered conical flask with 50 mL of synthetic wastewater and different amounts of adsorbent, during the selected time (5 days). Adsorption studies were performed with doses varying from 5 to 24 g L-1. After finishing the adsorption experiments, the solution was filtered through glass microfiber filter (1.2 µm). Results The adsorption capacity varies for rice straw ash from 31.91% up to 97.48% and rice straw ash with HCl from 17.49% up to 89.04%. An increase in temperature or dosage had a positive effect in the removal capacity, increasing its adsorption. Removal process of phosphorus was endothermic. Conclusion The use of rice straw ash could be a solution to reduce the phosphate in water bodies, providing an advantage to the proposed alternative of agro-waste management.

Purpose The research was focused on evaluating phytotoxicity of sewage sludge from two selected wastewater treatment plants in Czech Republic. Methods Laboratory experiments were carried out with samples of sewage sludge, which were focused on the evaluation of their phytotoxicity by using the PhytotoxkitTM testing set. Specifically, the inhibitory/stimulating effect was established on the growth of roots from the seeds of white mustard (Sinapis alba L.). The chosen proportions of sewage sludge were 10%, 30% and 50%. The test was conducted in three repetitions. Additionally, the research also included a comparison of the effect of compost addition to the sewage sludge and its potentially increased stimulating effect on the growth of roots from the seeds of white mustard (Sinapis alba L.). Ratios of compost were 5%, 15%, 25% and 50%. The test was conducted in three repetitions. Results Stimulating effect on the growth of white mustard (Sinapis alba L.) was demonstrated only in samples with the sludge proportion of 10%. The results also show that the addition of compost reduced phytotoxicity of sewage sludge in all three tested ratios (5%, 15%, 25% and 50%). Conclusion It was found out that the addition of compost resulted in the decreased phytotoxicity of all tested sewage sludge samples, and hence in their suppressed inhibitory effect.

Purpose To evaluate the feasibility of using biosolids and fly ash, processed through the Bokashi fermentation process, as growth promoters of maize. These two components were included because they are generated in large amounts and represent an environmental problem all over the world. Additionally, these materials have high concentrations of nutrients, but they have not been widely used because they also contain traces of heavy metals. Methods Components of regular Bokashi are as follows: soil, cow manure, chopped corn stalks, wheat bran, yeast, crushed charcoal, water and brown sugar. For this research, cow manure was replaced with biosolids, and charcoal was replaced with fly ash. The materials were mixed, inoculated with Saccharomyces cerevisiae and allowed to be fermented until the temperature stabilized. The maize plants were grown in four treatments: Bokashi with biosolids and fly ash, Bokashi with cow manure, chemical fertilizer and an unamended control. Results The plants grown in the Bokashi with biosolids and fly ash (BBFA) treatment had the highest aerial biomass (49.71 g), total biomass (69.82 g), N concentration (242 % higher than the control) and P concentration (94% higher than the control). Cadmium and lead concentrations were below the detection limits both in the soil amendments and in the tissue of maize plants. Conclusion Biosolids and fly ash processed by the Bokashi technique resulted in improved nutrition and growth of the maize plants. Through Bokashi fermentation, biosolids and fly ash can be safely used in agricultural or forestry applications.

Purpose The objective was to evaluate the effect of the application of composted and non-composted poultry litter, as fertilizer in agricultural areas, on the survival and reproduction of the springtails (Folsomia candida) through standardized ecotoxicological tests. Methods The treatments included in the application of composted and non-composted poultry litter on Entisol were in the following doses 0, 10, 20, 40, 60, 80, 100 t ha-1, for the lethality test, and 0, 5, 7.5, 10, 15, 30, 40, 60 t ha-1 for th e reproduction test. Results For the composted litter, the LC50 value was 76.45 t ha-1 and for EC50, it was 17.96 t ha-1. For the non-composted poultry litter, the values of LC50 was 43.12t ha-1 and EC50 value was 19.36 t ha-1. Conclusion The highest toxicity was observed in the non-composted litter, emphasizing the importance of stabilization of the organic compound before its use as fertilizer.