Magnesium-modified biochar was used to adsorb phosphorus from wastewater and used as a phosphorus source to be recycled to reduce the ammonia nitrogen of piggery digestive wastewater

High concentrations of ammonia nitrogen in piggery digestive wastewater are toxic to the microorganisms in wastewater treatment systems. The ammonia nitrogen load can be decreased by struvite precipitation. The purpose of this paper was to take phosphate from magnesium-modified biochar adsorbed wastewater as a phosphorus source and add it to biogas slurry to reduce the ammonia nitrogen concentration. The effects of phosphorus source dosage, initial reaction pH value and reaction time on ammonia nitrogen removal from biogas slurry were investigated, and then the subsequent biogas slurry underwent sequencing batch reactor biochemical treatment. When the phosphorus source dosage was 20 g/L, initial reaction pH value was 10.0 and reaction time was 1 h, the NH3–N recovery was 62.98%. The subsequent biogas slurry met the discharge standards (DB44/613–2009) after biochemical treatment. An innovative process for the recycling of pig farm waste, nitrogen and phosphorus recovery and advanced treatment of biogas slurry is first proposed in this paper.