Expanded Landfill in Guangdong employs the Landfill Leachate Treatment method

A 15-year-old landfill in Guangdong, China, recently expanded in order to comply with the latest regulation using a system comprising of membrane bioreactor (MBR) and nanofiltration (NF) methods as well as the new raw leachate. The plant, made by reverse osmosis (RO) system, is in operation producing a brine that needs to be managed and reduced.

Photo: The landflll lacheate treatment system used in an expanded Guangdong landfill

Landfill leachate treatment is gaining interest due to regulations that are getting stricter in several countries. Landfill leachate is produced by water percolation through garbage and is a very polluted effluent, characterised by high levels of ammonia, COD, salinity (chlorides and sulphates) and heavy metals.

Traditionally, common techniques applied to landfill leachate treatment are evaporation, membranes techniques, biological treatment and chemical-physical treatment. These technologies are chosen based on several aspects such as quality and analytical characteristics of the leachate, expected quality of the treated stream, quantity to treat and availability of some energy sources.

For this particular landfill, the inlet volume to the RO is 300 tonnes per day and the site produces about 2000 Nm3/h of biogas. Three biogas motors are thus installed producing 8MW of electrical power and thermal power constituting of a hot water stream. Normally, this stream is cooled down with air coolers etc, thus losing its thermal power. Instead, this free source, otherwise lost, can be employed to feed an evaporation plant for the treatment of leachate with very efficient global energy balance.

After some initial evaluations, only the evaporation system is considered to be most suitable for the management of the RO concentrate, considering the quality of this leachate is of high inorganic/ salty matrix. Evaporation has the capability to handle a liquid with a composition that changes both in products and in concentrations, also which is already pre-concentrated; badly polluted; has high final recoveries and concentrations;reduces final residue as much as possible; and produces a treated stream of high quality.

A process line consisting of two evaporation steps in series to maximise reduction of the polluted waste was thus proposed. The first stage is a forced circulation evaporator, namely the Evaled® AC F 20, while the Evaled® AC R 6, that is fed with the concentrate of the former, is a scraped unit consisting ofa very efficient heating system, which can achieve high concentrations with a semi-solid consistency of the final residue. The scraping system also assures the heat transfer when concentration increases significantly and semi-solid features are achieved. Both units are powered by the cogeneration system thus reaching an efficient energy balance.

The two-step process realises a global mass balance with 83 per cent recovery of the water. The implementation of an evaporation unit on this landfill site has resulted in improvements such as the reduction of the volume of the final residue to dispose, thus significantly reducing the associated costs for disposal; the production of a very high quality of treated water; the effectiveness of the combination of cogeneration and evaporation.

The recovery of thermal power from the cogeneration plant also provides the energy required to operate the evaporation system with a very low running cost. This combination of technologies provides an increase in the global efficiency of the landfill operations.