Investigating the use of aerobic granular sludge for removal of nitrogenous compounds for wastewater treatment in a recirculating aquaculture system

Abstract

Recirculating aquaculute system (RAS) is growing fast and becoming more attractive from sustainability perspective. The main goal in RAS is to use less water, achieve better waste management, improve nutrient loading, and have minimal negative environmental effects. One of the current challenges facing RAS is the nitrogen compounds in the effluent. Nitrogenous compounds have several ecological severe effects such as eutrophication, acidification, and toxicity to the marine environment. Nitrogen removal from aquaculture wastewater is vital to preserving marine life, to abide with the environmental regulations and to promote the growth of the industry.

In this master thesis, the aim is to examine nitrogen removal efficiency of aerobic granular sludge (AGS) to treat the effluent of RAS facility operated by the Natural Resources Institute Finland (LUKE). Based on the literature, AGS could treat various and wide ranges of wastewater compositions. Recent studies showed that total nitrogen (TN) concentration in the influent wastewater ranged from approximately 20 to 4000 mg/l, and removal efficiency was from 31 to 99.3%. The total phosphorus (TP) concentration in the influent wastewater ranged from 1.8 to 34.5 mg/l, and removal efficiency was from 36 to 97.7%.

Laboratory scale tests were carried out to study the feasibility of AGS for RAS wastewater. Experimental work proved the possibility of restoring the activity of granules after 64 days of storage. Preserving the bioactivity and physical characteristics during storage successfully promoted quick recovery of nutrients removal of AGS. The achieved removal of TN, TP and ammonia reached up to 94.5%, 83.7%, and 99.9%, respectively. Keeping the system in natural pH or between 7-8.5 is a safe and a good range for granules formation. Results confirmed the potential of AGS for RAS wastewater treatment.