Effects of bulking material types on water consumption and pollutant degradation in composting process with controlled addition of different liquid manures

The role of freshwater sludge and its carbonaceous derivatives in the removal of lead, phosphorus and antibiotic enrofloxacin: Sorption characteristics and performance

Freshwater sludge (FS) produced from drinking water treatment plants is generally filter pressed and disposed in the landfill. However, FS could be potentially reused. In this study, FS were processed into biochar and hydrochar via pyrolysis and hydrothermal carbonization, respectively. The sorption characteristics/mechanisms of FS and its derivatives (biochar-B300, B500 and B700 and hydrochar-H140, H160, H180 and H200) for the removal of three typical pollutants (i.e., lead (Pb), phosphorus (P) and enrofloxacin (ENR)) found in swine wastewater were investigated using batch adsorption tests and microstructural analyses. It was found that Pb sorption was relatively enhanced due to the increased electrostatic attraction and surface precipitation of Pb(OH)₂ while the anionic phosphate adsorption relatively decreased as a result of enhanced electrostatic repulsion at higher solution pHs. Comparatively, ENR adsorption was less affected by solution pH probably due to dominance of physical adsorption evidenced by the good fitting of the BET isotherm model (R² = 0.95). The maximum sorption capacities of Pb were in the order of B700≈B500 (71 mg/g)>B300 ~ FS(37 mg/g)>H140 ~ H160 (13 mg/g)>H180 ~ H200 (6 mg/g). The adsorption capacities for P were relatively lower: FS (47 mg/g)>B300 (38 mg/g)>H140 (27 mg/g)>B700 (37 mg/g)≈B500 (24 mg/g)≈H160 (23 mg/g)>H180 (16 mg/g)>H200 (14 mg/g). This study provides an understanding of the sorption characteristics and mechanisms of FS and its carbonaceous products for common cationic, anionic and organic pollutants and elucidates new insights into the reuse of FS for pollutant removal to achieve the waste-to-resource concept and enhance water quality, soil health and food safety.

Potential of windrow food and green waste composting in Tunisia

Solid waste management and disposal is one of the most significant challenges facing urban communities around the world. There is a wide range of alternative waste management options and strategies available for dealing with the notable increase in the waste stream. Composting is one of the most viable and efficient waste treatment options in terms of the reduction in the negative effects from the application of organic waste to soil. The experimental research aimed to examine the potential of producing compost from different organic waste streams in Tunisia. Two experimental windrow piles made from cooked and uncooked food and garden wastes were initiated and temporally monitored. The composting process was controlled in terms of temperature and moisture. Sampling was carried out over the period of the composting process. All of the collected samples were analyzed in terms of their physical, chemical, and biological properties; pH, C:N ratio, nitrification index (NI), microbiological tests, respiration activity (AT4), and heavy metal content. The quality of the final product was determined and compared with Tunisian and German standards. The findings demonstrated a significant reduction in the initial C:N ratio to about 15 by the end of the process. Additionally, the results showed that the compost produced appeared to be stable and was deemed to be class V finished compost; the NI was found to be around 1, while the AT4 was estimated to be lower than 6 mg O2/g TS. Regarding the heavy metal content, the final products were characterized as having a lower concentration than those values set by Tunisian and German standards.

Corn cobs efficiently reduced ammonia volatilization and improved nutrient value of stored dairy effluents

Dairy farms produce considerable quantities of nutrient-rich effluent, which is generally stored before use as a soil amendment. Unfortunately, a portion of the dairy effluent N can be lost through volatilization during open pond storage to the atmosphere. Adding of covering materials to effluent during storage could increase contact with NH₄⁺ and modify effluent pH, thereby reducing NH₃ volatilization and retaining the effluent N as fertilizer for crop application. Here the mitigation effect of cover materials on ammonia (NH₃) volatilization from open stored effluents was measured. A pilot-scale study was conducted using effluent collected at the Youran Dairy Farm Company Limited, Luhe County, Jiangsu, China, from 15 June to 15 August 2019. The study included seven treatments: control without amendment (Control), 30-mm × 25-mm corn cob pieces (CC), light expanded clay aggregate - LECA (CP), lactic acid (LA) and lactic acid plus CC (CCL), CP (CPL) or 20-mm plastic balls (PBL). The NH₃ emission from the Control treatment was 120.1 g N m^-2, which was increased by 38.1% in the CP treatment, possibly due to increased effluent pH. The application of CC reduced NH₃ loss by 69.2%, compared with the Control, possibly due to high physical resistance, adsorption of NH₄⁺ and effluent pH reduction. The lactic acid amendment alone and in combination with other materials also reduced NH₃ volatilization by 27.4% and 31.0-46.7%, respectively. After 62 days of storage, effluent N conserved in the CC and CCL treatments were 21.0% and 22.0% higher than that in the Control (P < 0.05). Our results suggest that application of corn cob pieces, alone or in combination with lactic acid, as effluent cover could effectively mitigate NH₃ volatilization and retain N, thereby enhancing the fertilizer value of the stored dairy effluent and co-applied as a soil amendment after two months open storage.

From anaerobic to aerobic treatment: upcycling of digestate as a moisturizing agent for in-vessel composting process

In Tunisia, there are crucial challenges facing both urban and rural areas, the most prominent of which are the production of organic waste, the need for waste treatment, the demand for water and energy and the need for a circular economy. To this end, the study was designed to develop a technical concept on closed cycle ‘biowaste to bioenergy’ treating, basically food waste (FW) through combined biological processes. In this approach, the generated digestate from FW anaerobic reactors was used successfully as a moisturizing agent for FW in-vessel composting. Four types of digestate were examined to be used as moisturizing agent (MA). The selection of the appropriate MA was achieved based on technical criteria; moisture content (MC), C:N ratio and heavy metals concentrations. The findings showed that the digestate obtained from anaerobic co-digestion of food waste and wheat straw (D1) was the most efficient AD-effluent to be added. In terms of composting process performance, the thermophilic phase of the amended reactor (A1) lasted 16 days and reached higher temperatures of about 72 °C, while the unamended one (A1) was characterized by a thermophilic temperature of around 66 °C indicating that the end products were of a pathogen-free compost. When it comes to the physico-chemical factors examined demonstrating that the biological conditions were sufficiently developed. The findings showed overall decreasing profiles during the composting period for moisture, C:N ratio as well as nitrification index (NI). From the quality-point of view, it was found that heavy metal concentrations had lower limits than those values set by German standards. Moreover, all the compost samples appeared to be stable and classified as class IV and V end product.

A novel lignin degradation bacteria-Bacillus amyloliquefaciens SL-7 used to degrade straw lignin efficiently

Using tobacco straw (Ts) and lignin as the sole carbon source, a strain was isolated from Ts and identified as Bacillus amyloliquefaciens SL-7 by 16S rDNA gene-sequencing technology.7-day incubation of Bacillus amyloliquefaciens SL-7 can reduce the chemical oxygen demand (COD) by 69.35% in lignin mineral salt medium. The activity of Manganese peroxidase (MnP) reached maximum level 258.57 U L^-1, and Lignin peroxidase (Lip) was 422.68 U L^-1 at 4th day. The highest Laccase (Lac) activity (55.95 U L^-1) was observed at 3th day. After straw-liquid fermentation degradation of 15 days, the bacterial could degrade 28.55% lignin of the straw which was close to that of fungi. Compared with the control group and effective microorganisms (EM) group, the lignin degradation rate in Bacillus amyloliquefaciens SL-7 group increased by 22.26% and 11.70% at 41-day compost fermentation of tobacco straw. These show the strain has strong lignin degradation performance.