This paper summarizes different operating aspects and experiences of several SHARON plants. The SHARON process is suitable for treatment of high strength ammonia wastewaters such as reject water from dewatering of digested sewage sludge and wastewater from sludge drying or incineration plants. The aerated retention time and nitrite concentration are the two most important process parameters to control the ammonia outlet concentration. Ammonia removal efficiencies can be over 95%, are variable and can be targeted according to the required needs of the main WWTP and/or to minimize overall nitrogen removal costs. The process is compact and simple to operate. Depending on site specific circumstances there are different system configurations possible. Nine years of operating experience prove that the SHARON process is sustainable and highly competitive. Compared to conventional techniques there are significant savings of energy and consumables. Application of fine bubble aeration has further decreased aeration costs. Recently the use of by-products of the biofuel industry as COD source for denitrification has further increased the cost effectiveness. SHARON is successfully applied to significantly improve the main WWTP nitrogen effluent quality. It proves to be a cost effective alternative for conventional extension of the WWTP.
The SHARON process was developed in the 90’s of the last century at the Delft University of Technology (Hellinga et al., 1998; Hellinga et al., 1999; STOWA, 1996). SHARON refers to Stable and High activity Ammonia Removal Over Nitrite. The process is especially suitable for high strength ammonia wastewaters. Typical applications are treatment of reject water from dewatering of digested sewage sludge (Mulder et al., 2001; Kempen et al., 2001) and wastewater from sludge drying or incineration plants. By treating reject water which is only 1% of the hydraulic load of a WWTP, the nitrogen load to a WWTP is reduced by 10 to 30%. With side stream treatment the overall nitrogen removal efficiency of the WWTP can be significantly improved. Other applications are treatment of landfill leachate and wastewater from digestion of organic waste and manure (Notenboom et al., 2002).
The SHARON process makes advantage of the difference in growth rate of ammonia oxidizers and nitrite oxidizers which is illustrated in Figure 1. At higher temperatures, the ammonia oxidizers have a significant higher growth rate. By controlling the aerated retention time to approximately 1 day, the nitrite oxidizers will be washed out of the tank, and nitrification will be limited to nitrite formation. The SHARON process is operated in completely mixed reactors without sludge retention. Therefore the hydraulic retention time (HRT) is equal to the sludge retention time (SRT). A system without sludge retention behaves like a chemostat. Typically the outlet concentration of a chemostat is independent of the inlet concentration. A chemostat is therefore especially suited for treatment of high strength wastewaters. Furthermore the absence of sludge retention makes the SHARON process insensitive to suspended solids levels that may vary in reject water of sludge dewatering.