The anaerobic digestion process produces methane while stabilizing sludge. As of 2020, 62 anaerobic digesters in public wastewater treatment plants are operational in Korea. Many researchers have studied to improve digester performance. Thermal hydrolysis technology is one of the pre-treatment methods for treating sludge. Reduced retention time and enhanced biogas production are the main advantages of sludge disintegration at relatively high temperatures and pressures. But nutrients like nitrogen and phosphorus are released from the pre-treated sludge. Phosphorus is a non-renewable resource that is essential to food production. Wastewater receives 20% of the total phosphate discharge, while 90% of the influent phosphorus load is in sludge. For efficient phosphorus recovery, it is essential to comprehend the phosphorus release characteristics during wastewater treatment, including anaerobic digestion. Biological or chemical processes can achieve phosphorus removal to comply with the effluent discharge limits regulations. The three primary sources of phosphorus in sludge are aluminum-bound phosphorus (Al-P), polyphosphate in phosphorus-accumulating organisms (PAOs), and iron-bound phosphorus (Fe-P). Anaerobic digestion is the typical method for recovering carbon and phosphorus. However, previous research has demonstrated that most phosphorus in anaerobic digestion occurs as a solid phase coupled with heavy metals. Therefore, the poor mass transfer rate results in a slow phosphorus release. Due to the recent growth in interest and significance of phosphorus recovery, many researchers have studied to improve the quantity of phosphorus released into the liquid phase through chelation addition, process operation optimization, and disintegration using sludge pre-treatment. The study aims to investigate characteristics of the phosphorus release associated with the thermal hydrolysis breakdown of sludge and propose a method for recovering phosphorus in a wastewater treatment plant. When solubilizing sludge using thermal hydrolysis pre-treatment, organic phosphates, inorganic phosphates, and polyphosphates are converted into ortho-phosphate. Therefore, applying thermal hydrolysis, anaerobic digestion, and phosphorus recovery processes (struvite formation or microbial electrolysis cells) can recover carbon and phosphorus.

Response surface methodology (RSM) based on a Box-Behnken Design (BBD) was applied to optimize the thermal-alkaline pre-treatment operating conditions for anaerobic digestion of flotation scum in food waste leachate. Three independent variables such as thermal temperature, NaOH concentration and reaction time were evaluated. The maximum methane production of 369.2 mL CH4/g VS was estimated under the optimum conditions at 62.0°C, 10.1% NaOH and 35.4 min reaction time. A confirmation test of the predicted optimum conditions verified the validity of the BBD with RSM. The analysis of variance indicated that methane production was more sensitive to both NaOH concentration and thermal temperature than reaction time. Thermal-alkaline pretreatment enhanced the improvement of 40% in methane production compared to the control experiment due to the effective hydrolysis and/or solubilization of organic matters. The fractions with molecular weight cut-off of scum in food waste leachate were conducted before and after pre-treatment to estimate the behaviors of organic matters. The experiment results found that thermal-alkaline pre-treatment could reduce the organic matters more than 10kD with increase the organic matters less than 1kD.

구제역 등 가축전염병 발병으로 인한 가축 사체 살 처분 시 병원균의 확산 및 전파를 방지하기 위해 매몰, 소각, 렌더링, 퇴비화, 알칼리 가수분해 및 혐기성 소화 등의 방법을 이용하여 폐기 처리하여야 한다. 매몰에 의한 살 처분은 전 세계적으로 가장 선호되는 방법이다. 우리나라의 경우, “가축전염병예방법 제 20조”, “가축전염병예방법 시행규칙 제 25조” 및 긴급방역행동지침(가금인플루엔자, 전염성해면상뇌증 및 구제역 등)에 의해 가축전염병에 전염된 가축 사체에 대해서는 대부분 매몰하는 방식으로 처분하고 있다. 가축 사체는 매몰 초기, 호기 조건에서 분해가 이루어지나 이를 제외한 기간에는 혐기 조건에서 분해가 이루어진다. 폐기물의 호기성 분해는 혐기성 분해에 비해 안정화를 촉진시키는 데 효과적인 것으로 알려져 있다. 본 연구에서는 가축 사체를 매몰한 모형매몰지를 호기 및 혐기 조건으로 운영하여 이에 따른 안정화 특성을 파악하였다. 호기성 모형매몰지의 침출수 발생량은 혐기성 모형매몰지에 비해 약 1.4배 많은 것으로 나타났으며 침출수 발생속도는 약 1.5배 빨라진 것으로 나타났다. 또한 총유기탄소를 기반으로 한 가축 사체의 분해율을 살펴보면, 호기성 모형매몰지에서 약 1.9배 높은 것으로 나타났으며 발생된 총유기탄소의 약 74%는 침출수를 통해 발생된 것으로 나타났다. 본 연구 결과, 가축 사체의 호기성 분해는 혐기성 분해에 비해 안정화에 효과적인 영향을 미치는 것으로 나타났으나 분해 시 발생되는 악취 또는 에어로졸 등에 대한 해결 방안이 필요할 것으로 판단된다.