Proceedings

A Technical Review of The Emerging Technologies for Treating Dewatering Liquors & Process Reject Water

Bungay, S., Helix ECL

(free)

Abstract Over the last 20 years a number of biological treatment processes have emerged for treating high-strength ammonia liquors. In the water sector, the main four sources of high-strength ammonia liquors are leachate from landfill sites; and the dewatering liquor arising from municipal Anaerobic Digestion (AD) plants, Advanced Anaerobic Digestion (AAD) plants, and commercial Biowaste Anaerobic Digestion (BAD) plants.

As environmental standards have become more stringent, and the number of Advanced Anaerobic Digestion have increased; the requirement for side-stream treatment liquor treatment has concomitantly increased. The early liquor treatment plants were designed for complete nitrification; converting the high-strength ammonia liquor to nitrate. Over the last decade treatment processes have emerged for nitrification & denitrification, partial nitrification (nitritation) & partial denitrification (denitritation), and short-circuiting of the nitrogen cycle with partial nitrification and the conversion of ammonium directly into nitrogen (N2) gas.

This paper discusses the variety of technologies that have emerged over the last 20 years such as specific leachate treatment plants, AMTREAT, Anammox, ANITA, DEMON, and the SHARON process; and details their suitability for treating different reject liquors; their requirements for flow and load balancing, process instrumentation, and process heating/cooling.

Key Words: AMTREAT, Anammox, ANITA, CANON, DEMON, Denitrification, Leachate, Nitritation, Nitratation, SHARON.

Introduction Process reject liquors containing high concentrations of ammonia can be produced from a variety sources. In the water sector, the main four sources of high-strength ammonia liquors are leachate from landfill sites; the dewatering liquor arising from municipal Anaerobic Digestion (AD); dewatering liquors arising from Advanced Anaerobic Digestion (AAD) plants; and dewatering liquors arsing from commercial Biowaste Anaerobic Digestion (BAD) plants.

During the last 30-years, more than 100 aerobic biological leachate treatment plants have been constructed on UK landfill sites which produce a leachate with an ammoniacal-N concentration often in excess of 2,000 mg/l NH3-N [1]. There are more than 500 municipal mesophilic anaerobic digestion (MAD) plants processing over 700,000 tonnes of dry sludge per year [2]. Conventional MAD produces a digestate that typically contains aqueous ammoniacal-N concentrations of 500 to 1,000 mg/l. If the digestate is dewatered to produce a caked product, the aqueous ammonia will be present in the dewatering process reject water or liquor.

As the number of municipal Advanced Anaerobic Digestion (AAD) and commercial Biowaste Anaerobic Digestion (BAD) plants have increased, there has been an associated increase in the ammonia concentrations contained in the process dewatering liquors. At AAD plants, the anticipated concentration of ammonia is in the range 1,500 – 3,500 mg/l, whereas at BAD plants ammonia concentrations in excess of 5,000 mg/l have been encountered.

At municipal Sewage Treatment Works (STW), the traditional treatment strategy for these liquors has been to pass them back to the existing treatment works. However, with the increasing implementation of tighter and total nitrogen limits, and the increasing ammonia concentrations, this practice may not be feasible because such plants often have insufficient nitrifying capacity. Landfill sites and commercial BAD plants tend to be stand-alone plants, so there is not a STW to return the liquors to. Therefore, in all four applications there has been a move to treat reject liquors at a separate, dedicated plant.

There are a variety of processes for treating high-strength ammonia liquors including physicochemical and biological methods; stripping and scrubbing, biological nitrification and denitrification; and physical separation processes. This paper discusses the biological treatment processes that have emerged over the last 20 years such as specific leachate treatment plants, AMTREAT, SHARON, Anammox, ANITA, and DEMON; and details their suitability for treating different reject liquors; their requirements for flow and load balancing, process instrumentation, and process heating/cooling.

 

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