Innovative approach to centrate nitrification accomplishes multiple goals: nitrogen removal and odour control

Abstract

In 2001, the City of Phoenix, Arizona (USA) committed to the conversion of the existing high-rate anaerobic digestion process at the 8.9 m(3)/s 91st Avenue Wastewater Treatment Plant (WWTP) to a multi-phase process (acid/methane, mesophilic/thermophilic) to optimise existing digestion capacity and achieve Class A biosolids. The improved solids reduction is anticipated to double the ammonia load in the sludge dewatering liquor (centrate), which is currently treated in the nitrification/denitrification (NdeN) activated sludge facilities. In order to continue to meet the plant total nitrogen discharge limit of 10 mg/L as N, a separate centrate nitrification system was incorporated into the plant's process flow scheme to efficiently manage the high ammonia recycle stream. By discharging the nitrified centrate to the plant headworks, an added benefit of reduced hydrogen sulfide (H(2)S) emissions was realised to approximately $310 (USD).

Sidestream Treatment of Anaerobically Digested Sludge Centrate Using Activated Sludge and Aerobic Granular Sludge Sequencing Batch Reactors

“…In cold climates, some WWTPs are able to treat centrate returned to the mainstream, but the winter months may cause fluctuations in effluent total nitrogen concentrations (Husband et al, 2010;Stenström & La Cour Jansen, 2016). At full scale, there are limited applications of sidestream nitrification.…”

“…(2010) reported on how the implementation of sidestream centrate nitrification emanated multiple environmental benefits. A 50% conversion of ammonia to NOx-N (NO2-N + NO3-N) was achieved without the addition of supplemental alkalinity and gaseous hydrogen sulfide (H2S) concentration entering the odour control scrubber in the headworks was reduced by 70% (Husband et al, 2010). Since nitrate salts are an established solution to wastewater odour control, the presence of nitrite and nitrate in the sidestream effluent provided an oxygen-rich environment that decreased the formation and emission of H2S (Husband et al, 2010).…”

Sewage Treatment Plants

“…On the other hand, in ASD systems the malodourous emission is employed for wastewater oxygenation by directly sparging the emission into the aeration tank of the plant. The only study regarding this strategy estimated savings of 310 USD per day in odour treatment by the implementation of nitrified centrate recycling (Husband et al 2010). Odour REs > 99% have been recorded in largescale WWTPs treating the odorous emissions in their aeration tanks (Kiessewetter et al 2012;Lebrero et al 2011;Barbosa et al 2006).…”

Gaseous Emissions from Wastewater Facilities

“…The implementation of the centrate nitrification system (activated sludge system) at the 91 st Avenue WWTP in Phoenix, Arizona showed an added benefit of reduced H 2 S emission in addition to nitrogen removal (Husband et al, 2010). The treated centrate, containing high concentrations of NO x -N (nitrates and nitrites), was discharged to the plant headworks which provided an oxygen source for oxidizing H 2 S and preventing its formation.…”