Rapid Startup of Aerobic Granular Sludge Using Cationic Polymer For Industrial Wastewater Treatment

The conventional activated sludge (CAS) process is used worldwide for municipal and industrial wastewater treatment. This technology has been used for over 100 years, providing sanitation and minimizing environmental damage. However, the approach is no longer deemed sustainable due to its extensive land footprint, recirculation flows, and complex process designs that demand multiple units for the removal of carbon, nitrogen, and phosphorus from wastewater. The CAS process currently faces a critical challenge to its viability due to existing bottlenecks and recent advancements in sustainable wastewater treatment. The primary factors driving sustainable wastewater treatment technologies include enhancements in the treatment process, reduction of resource inputs, and recovery of resources from wastewater. An aerobic granular sludge sequencing batch reactor (AGS SBR) was developed to address the nutrient removal and solid-liquid separation challenges associated with the conventional activated sludge (AS) process. AGS technology tackled the primary limitations of the AS process, such as extensive land requirements, significant energy demands for biomass and wastewater recirculation, and challenges related to biomass-water separation. Aerobic granules are dense, spherical microbial aggregates that form independently without the need for attachment media. They possess a compact and robust microbial structure, excellent settling properties, high biomass retention, and resilience to toxic substances and shock loading. Compared to flocculent sludge cultures, aerobic granules enable faster wastewater treatment within a significantly smaller footprint. Despite the advantages and potential of aerobic sludge granulation, the underlying mechanisms driving aerobic granulation remain poorly understood, and aerobic granules often exhibit limited stability, which constrains their practical application in wastewater treatment. The formation of stable aerobic granules is essential for effective wastewater treatment, but initiating an aerobic granular system from conventional activated sludge typically requires several weeks. Such a long startup time may cause a problem for the implementation of aerobic granulation for industrial applications. By considering these limitations, hydrofloc cationic polymer C4400SA was used to enhance the stability and rapid formation of aerobic granules. The laboratory research work was divided into four phases; in the first phase, Laboratory experimental work was designed and implemented. Cationic polymer with 15 mg/L of dosage was used in the lab scale reactor to cultivate granules rapidly. The polymer dosage was used in each phase of the research except phase IV. The system was fed with real industrial wastewater and operated for 80 days. The AGS system transformed floccular sludge into aerobic granules after 10 days. However, instability of granules was observed at the end of the experiment. The removal efficiency of TP, TN, NH4+ –N, total COD, and soluble COD was observed at 62%, 73%, 97%, 93%, and 79%, respectively. The average particle size of 0.6-09 mm was observed in the system. In phase II, the anaerobic phase of 60 minutes was introduced in each cycle of the operation of the reactor. Our purpose was to get mature and stable granules because, in the first phase, we had an issue with the stability of the granules. The system progressed well with these conditions. Dense, compact, and stable granules were obtained with good removal efficiency of pollutants. The average particle size of granules was 1.9-2.2 mm, which was better than phase I. In phase III, the reactivation and performance of stored granules treating real industrial wastewater were observed. The mature granules of Phase II with an average size of 2-2.2 mm were stored in tap water at 4°C for 30 days. After 30 days, the granules were used in the AGS system to check the stability and performance of the granules after reactivation. Stored granules were reactivated after 10 days of the operation of the reactor and showed mature granules with an average size of 2.8-3 mm. In phase IV, the ASG system was developed to treat real textile wastewater. The research activity was carried out at Universiti Tun Hussein Onn Malaysia for 70 days. In this phase, similar strategies were followed as in phase II. The system showed good removal efficiency of organic pollutants. For the removal of color, a dicyandiamide formaldehyde (DCF) decoloring agent was used which resulted in over 90% removal. For 44-58 days of operation of the reactor, the removal efficiency of organic pollutants was disrupted due to the decoloring agent. However, after 58 days, the system became stable at the end of the experiment. In summary, the research concluded that the AGS SBR enhanced with cationic polymer addition offers a sustainable solution for industrial wastewater treatment. The AGS SBR presents a potentially superior alternative to the conventional activated sludge (CAS) process.