Question

4. Why it is advisable to use organic manure instead of chemical fertilizers and to
neutralize industrial wastes before releasing into water bodies?​

Answer 1

Agriculture and Economic Benefits of Compost

The application of chemical fertilizers can increase the crop yields quickly, but they also could cause soil hardening and decrease soil organic matter and pH after a long period of application, resulting in loss of soil productivity [55]. However, most proportion of the chemical fertilizers will be ran off or leached due to rain and heavy irrigation, consequently leading to environmental pollution and lower fertilizer effect. Compost is produced from organic waste, which not only contains organic matter but also is rich in micro- and macronutrients. The utilization of compost as a soil fertilizer or amendment could restore the soil quality and improve soil structure and fertility, which not only serves an important role in agricultural production but also is of great significance for improving the ecological environment [56]. Nowadays, using compost as a substitute to chemical fertilizer has become a global consensus. The application of compost could promote soil productivity and improve the crop quantity and quality, as well as increase the income of the farmers.

Answer 2

Answer:

Abstract

The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste materials and side flows is required to be more effective. In this research, a chemical precipitation method to simultaneously remove ammonium and phosphate from the reject water of anaerobic digestion plant using calcined paper mill sludge and fly ash as a precipitant, was tested. Paper mill sludge is a waste material formed in the paper-making process, and fly ash is another waste material formed in the power plant. Objective of this research was to test whether these industrial waste streams could be used as low cost precipitation chemicals for ammonium and phosphate removal from wastewaters and whether the precipitate could be suitable for fertilizer use. Results indicated that calcined paper mill sludge had high removal efficiency for both ammonium (97%) and phosphate (73%). Fly ash also had good removal efficiency for both ammonium nitrogen (74%) and phosphate (59%) at 20 ± 2 °C. The precipitates contained high concentrations of nitrogen and phosphate and could be used as a recycled fertilizer. Other possible mechanisms for the removal of phosphate and ammonium were considered.

Graphic Abstract