Improvement of nutrient removal and phosphorus recovery in the anaerobic/oxic/anoxic process combined with sludge ozonation and phosphorus adsorption

Abstract

The effects of ozonation conditions on the performance of a continuous anaerobic/oxic/anoxic (A/O/A) process with sludge ozonation and phosphorus adsorption were investigated. In this system, excess sludge was ozonated by microbubble ozonation, and then the supernatant of the ozonated sludge was flowed into a phosphorus adsorption column packed with zirconium-ferrite adsorbent. The effluent from the column and the settlings of the ozonated sludge were recirculated in the A/O/A process. Long-term operation of a lab-scale system treating rural wastewater showed that ozonation affected not only the sludge reduction efficiency but also the nitrogen removal efficiency. When the amount of sludge to be ozonated was set at 16% of total MLSS per day, no excess sludge was withdrawn, but the nitrogen removal efficiency was deteriorated. Decreasing the amount of sludge to be ozonated (to 9.4% of total MLSS per day) resulted in efficient nitrogen removal, but the MLSS concentration increased slightly. Phosphorus accumulated in the sludge was re-solubilized by ozonation, and a large part of the solubilized phosphorus consisted of Pi. Almost all Pi was recovered in the phosphorus adsorption column.

Holistic sludge management through ozonation: A critical review

“…Ozonated sludge supernatant, has elevated concentrations of COD (Section 4.1.1), nitrogen (Section 4.1.2), and phosphorous (Section 4.1.3), and is a potential source where they could be retrieved. Thus far, the continuous recovery of phosphorous from ozonated sludge supernatant has been successfully achieved in several studies (Kondo et al, 2009;Qiang et al, 2015;Tsuno et al, 2008). There is also potential for other resources such as COD to be recovered or reused with the help of ozonation technology.…”

“…Other studies report that the majority (e.g., 80%) of solubilized phosphorous was in the form of orthophosphate (Kondo et al, 2009;Qiang et al, 2015). Secondly, decreasing sludge withdrawal allows phosphorous to accumulate in the reactors (Gardoni et al, 2011;Nie et al, 2014;Qiang et al, 2015) (Table 4).…”

“…The process removed 85% of influent phosphorous and recovered 80% of solubilized phosphorous through the adsorption column, but had a slight deterioration of total organic carbon (TOC) removal due to sludge solubilisation. Kondo et al, (2009) reported that a zirconium ferrite column recovered 90% of phosphorous solubilized by ozonation. Phosphorous recovery decreased when the adsorbent reached its maximum adsorption capacity, but the column was easily reactivated using acid solution and regained its previous performance.…”

“…For instance, Kondo et al, (2009) reported that increasing the amount of ozonated sludge (3.4-8.4 L/day) increased organic carbon loading and dissolved oxygen competition between nitrifying and heterotrophic bacteria. This phenomenon consequently decreased nitrification efficiency, which increased the concentration of ammonia (Kondo et al, 2009). Sui et al, (2014) observed that adjusting ozone concentration and flow rate could vary the conversion rate of solubilized organic nitrogen to ammonia.…”

“…Phosphorous recovery decreased when the adsorbent reached its maximum adsorption capacity, but the column was easily reactivated using acid solution and regained its previous performance. Available literature suggests that adsorption (80-90%) (Kondo et al, 2009;Suzuki et al, 2006) achieves a higher recovery of solubilized phosphorous than crystallization (30-75%) (Qiang et al, 2015;Tsuno et al, 2008). Furthermore, adsorption is potentially a more cost-effective approach than crystallization because adsorption columns can be reactivated and reused (Kondo et al, 2009).…”