Ammonia uptake by natural zeolite in municipal solid waste compost

Effectiveness of Biochar and Zeolite Soil Amendments in Reducing Pollution of Municipal Wastewater from Nitrogen and Coliforms

A greenhouse experiment with soil cores and wastewater application was carried out to investigate the effects of biochar and zeolite on the mobility of nitrogen and coliform bacteria during the leaching of columns repacked by a silty loam soil. Triticum aestivum plants were grown in cores with and without biochar and zeolite irrigated with municipal wastewater for 4 months in the greenhouse. Cores were then flushed with 800 mLof distillate water and, finally, the leachate was collected. Application of biochar or zeolite significantly (p ≤ 0.05) reduced nitrate and ammonium loss in soil after leaching process, compared to their non-treated counterparts. In addition, interactions of biochar and zeolite significantly decreased nitrate and ammonium content in leachate. Biochar had higher removal effects of coliform bacteria in leachate than zeolite. Lower nitrate and ammonium content in leachate was related to the increased retention of soil amendments. Application of 5% w/w of biochar also reduced the volume of leachate by 11% compare to control, but using 5% w/w and 10% w/w of zeolite increased the volume of leachate compared with non-treated columns by 21% and 48%, respectively. Taken together, these data highlight the need to consider the potential benefits of biochar and zeolite as soil amendment to reduce nitrogen mobility and remove coliform bacteria in the leaching process of municipal wastewater in agricultural systems.

Increased retention of available nitrogen during thermal drying of solids of digested sewage sludge and manure by acid and zeolite addition

Thermal drying is an increasingly common post-treatment for digestate-solids, but prone to N losses via ammonia (NH₃) volatilization. Acidification with strong acids prior to drying may retain ammonium (NH₄⁺) in the solids. Natural zeolites can provide adsorption sites for exchangeable cations as ammonium and porosity for free ammonia, which has the potential to contribute to higher N retention in the dried solids. The present study investigated whether the zeolite addition increases NH₄⁺-N retention during thermal drying of two digestate solids (manure based, MDS; sewage sludge based, SDS), and whether any synergistic effects of combining acidification with sulfuric acid and the addition of zeolite exist. Operating conditions included four pH levels (non-acidified control, adjusted to 8.0, 7.5, 6.5 with concentrated sulfuric acid), four zeolite addition rates (0%, 1%, 5% and 10%), fixed drying temperature (130 °C) and fixed air ventilation rate (headspace exchange rate of 286 times hour^-1). Zeolite addition significantly increased NH₄⁺-N retention from 18.0% of initial NH₄⁺-N in the non-acidified control up to a maximum of 57.4% for MDS, and from 76.6% to 94.5% for SDS. No positive synergistic effect between acidification and zeolite addition was observed, with acidification being the dominant. Nevertheless, zeolite has the potential to be a safe and easy-to-handle alternative to concentrated sulfuric acid.

The concept of circular economy strategy in food waste management for the optimization of energy production through anaerobic digestion

Food waste management (FWM) is considered to be an extremely important social issue besides an environmental one. Worldwide, it is estimated that 1.3 billion t/year of foods are disposed of in landfills (including edible and inedible foods). Moreover, FAO indicated that if food waste (FW) was a country, it could be the 3rd biggest CO₂ producer after China and the USA with more than 3.5-4.2 billion of t equivalence CO₂. Each citizen in the entire EU produces approximately 179 kg/year FW equal more or less with 600 €/year. This paper focuses on the concept of circular economy (CE) and how can we optimize and improve the production of biogas from UASB-R (upflow anaerobic sludge blanket reactor) using FW and natural minerals (clinoptilolite). The study was elaborated through laboratory scale experiments using different mixtures of FW, liquid waste from slaughterhouse (LWS), and natural clinoptilolite (Cli). The amount of biogas produced and the methane content of biogas were used as indicators in order to monitor and asses the performance of the anaerobic digester. The results of the present study were encouraging towards the use of FW in existing anaerobic treatment plants, suggesting selective collection at source of FW, diversion from landfills, and use as a secondary resource for energy recovery through a transition to a CE. The results indicate that the use of FW with zeolite duplicates the production of CH₄ within the same days of production compared with the control sample.

Using natural clinoptilolite zeolite as an amendment in vermicomposting of food waste

The effect of adding different proportions of natural clinoptilolite zeolite (5 and 10%) to food waste vermicomposting was investigated by assessing the physicochemical characteristics, worms' growth, and maturation time of finished vermicompost in comparison with the vermicompost prepared with no amendment (control). Vermicomposting was performed in 18 plastic containers for 70 days. The experimental results showed that the carbon-to-nitrogen (C/N) ratios were 15.85, 10.75, and 8.94 for 5 and 10% zeolite concentration and control after 70 days, respectively. The addition of zeolite could facilitate organic matter degradation and increase the total nitrogen content by adsorption of ammonium ions. Increasing the proportion of zeolite from 0% (control) to 10% decreased the ammonia escape by 25% in the final vermicompost. The natural zeolite significantly reduced the electrical conductivity (EC). At the end of the process, salinity uptake efficiency was 39.23% for 5% zeolite treatment and 45.23% for 10% zeolite treatment. The pH values at 5 and 10% zeolite-amended treatments were 7.31 and 7.57, respectively, in comparison to 7.10 in the control. The maturation time at the end of vermicomposting decreased with increasing zeolite concentration. The vermicompost containing 5 and 10% zeolite matured in 49 and 42 days, respectively, in comparison to 56 days for the control. With the use of an initial ten immature Eisenia fetida worms, the number of mature worms in the 10% zeolite treatment was 26 more than that in the 5% zeolite treatment (21 worms) and 9 more than that in the control treatment (17 worms). Significantly, natural zeolite showed a beneficial effect on the characteristics of the end-product when used in the vermicomposting of food waste.

Resource recovery of food waste through continuous thermophilic in-vessel composting

In the Kingdom of Saudi Arabia (KSA) and Gulf region, a very small amount of municipal solid waste (MSW) is treated for compost production. The produced compost through traditional methods of compost piles and trenches does not coincide with the international standards of compost quality. Therefore, in this study, a continuous thermophilic composting (CTC) method is introduced as a novel and efficient technique for treating food waste into a quality compost in a short period of time. The quality of the compost was examined by degradation rates of organic matter (OM), changes in total carbon (TC), ash contents, pH, dynamics in ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N), and nitrification index (NI). The results showed that thermophilic treatment at 60 °C increased the pH of the substrate and promoted degradation and mineralization process. After 30 days of composting, the degree of OM degradation was increased by 43.26 and 19.66%, NH₄-N by 65.22 and 25.23%, and NO₃-N by 44.76 and 40.05% as compared to runs treated at 25 and 40 °C, respectively. The stability of the compost was attained after 30 to 45 days with quality better than the compost that was stabilized after 60 days of the experiment under mesophilic treatment (25 °C). The final compost also showed stability at room temperature, confirming the rapid degradation and maturation of food waste after thermophilic treatment. Moreover, the quality of produced compost is in line with the compost quality standard of United States (US), California, Germany, and Austria. Hence, CTC can be implemented as a novel method for rapid decomposition of food waste into a stable organic fertilizer in the given hot climatic conditions of KSA and other Gulf countries with a total net saving of around US $70.72 million per year.

Study and assessment of segregated biowaste composting: The case study of Attica municipalities

This work aims to assess the operation of the first large scale segregated biowaste composting scheme in Greece to divert Household Food Waste (HFW) from landfill and produce a material which can be recovered and used as compost. The source separation and collection of HFW was deployed in selected areas in Attica Region serving about 3700 households. Sorted HFW is collected & transported to the Mechanical and Biological Treatment (MBT) plant in Attica Region that has been designed to produce Compost Like Output (CLO) from mixed MSW. The MBT facility has been adjusted in order to receive and treat aerobically HFW mixed with shredded green waste in a dedicated composting tunnel. The composting process was monitored against temperature, moisture and oxygen content indicating that the biological conditions are sufficiently developed. The product quality was examined and assessed against the quality specifications of EU End of Waste Criteria for biowaste subjected to composting aiming to specify whether the HFW that has undergone recovery ceases to be waste and can be classified as compost. More specifically, the heavy metals concentrations (Cr, Cu, Ni, Cd, Pb, Zn and Hg) are within the set limits and much lower compared to the CLO material that currently is being produced at the MBT plant. In regard to the hygienic requirements of the product it has been found that the process conditions result in a pathogen free material (i.e. E. Coli and Salmonella) which does not favor the growth of viable weeds and plant propagules, while it acquires sufficient organic matter content for soil fertilization. Noticeable physical impurities (mainly fractions of glass) have been detected exceeding the quality control threshold limit of 0.5% w/w (plastics, metals and glass). The latter is related to the missorted materials and to the limited pre-treatment configurations prior to composting. The above findings indicate that effective source separation of biowaste is prerequisite for good quality production and marketing of compost and special consideration should be made to minimize glass impurities prior composting (i.e. awareness raising and pretreatment stage). Therefore, it is feasible to gradually replace the production of questionable quality CLO in MBTs with biowaste compost which is in line with the required quality control standards especially when heavy metals concentrations is concerned.

Composting domestic sewage sludge with natural zeolites in a rotary drum reactor

This work aimed the influence of zeolites addition on a sludge-straw composting process using a pilot-scale rotary drum reactor. The type and concentration of three commercial natural zeolites were considered: a mordenite and two clinoptilolites (Klinolith and Zeocat). Mordenite caused the greatest carbon removal (58%), while the clinoptilolites halved losses of ammonium. All zeolites removed 100% of Ni, Cr, Pb, and significant amounts (more than 60%) of Cu, Zn and Hg. Zeocat displayed the greatest retention of ammonium and metals, and retention efficiencies increased as Zeocat concentration increased. The addition of 10% Zeocat produced compost compliant with Spanish regulations. Zeolites were separated from the final compost, and leaching studies suggested that zeolites leachates contained very low metals concentrations (<1 mg/kg). Thus, the final compost could be applied directly to soil, or metal-polluted zeolites could be separated from the compost prior to application. The different options have been discussed.

The effects of natural zeolite on salinity level of poultry litter compost

The aim of this study was to investigate the salinity uptake by natural zeolite when used as an ingredient during the composting process. The amounts of 5% and 10% of natural zeolite were applied to poultry litter as volume and compared with the compost made with no amendment. The results clearly showed that the salinity level of poultry litter was too high. It was found that the salinity level in the end compost decreases with increasing the amount of natural zeolite used. Salinity uptake efficiencies were 66.64% and 88.92% for end product containing 5% and 10% natural zeolite, respectively. Significantly, the addition of natural zeolite to poultry litter compost was found to have a beneficial effect on the characteristics of the end product.