Recycling of Nitrogen and Phosphorus from Urban Wastewater Using Calcium-Silicate-Hydrate: A Case Study in Cambodia

Abstract

The main goal of this research study was to evaluate the calcium-silicate-hydrate (CSH) synthesized from calcium hydroxide (Ca(OH)₂) and rice husk charcoal and to determine if the CSH is economically and environmentally friendly and can be used as a promising strategy for nitrogen and phosphorus recovery. The CSH material was prepared by combining Ca(OH)₂ and rice husk charcoal in a 1:4 ratio and mixing the sample with 75% deionized water. Following mixing, a vibrator was used for 1 minute for Case 1, 2 minute for Case 2 and 3 minute for Case 3. The CSH was then put into molds which were maintained at room temperature for 3 weeks before starting the experiments. The two weeks adsorption experiment investigated parameters such as pH, EC, Ca, K, NH ₄⁺, and PO ₄^3- in 2 weeks. The 1^st and 2^nd elusion experiments were carried out on used CSH to test the dissolution rate of NH ₄⁺ and PO ₄^3-. To confirm the used CSH effectiveness as a fertilizer, a plant growth experiment was also carried out to measure the growth rate of spinach and the improvement of soil fertility. The results of the adsorption experiment indicated that CSH can effectively remove nutrients from wastewater, achieving removal rates of 97% for NH ₄⁺ and 98% for PO ₄^3-. The adsorption capacity of CSH is 0.065 mg- NH ₄⁺/g-CSH and 0.11 mg-PO ₄^3-/ g-CSH. Additionally, the used CSH can release 3-5 mg/kg for NH ₄⁺ and 6.6-7.7 mg/kg of PO ₄^3- in the elusion experiments. Moreover, the plant growth experiment also indicates that the soil fertility increased 3 times with the 5% addition of used CSH treatment, compared to the control treatment. These results suggest that CSH, made from Ca(OH)₂ and rice husk charcoal, could serve as a cost-effective solution to wastewater treatment and production of fertilizer for agricultural production.