Leachate and Wastewater Treatment Technology

Methods of wastewater treatment

 

In the last few decades, many approaches have been adopted to solve the problems associated with the treatment of leachate and wastewater. With the latter, the composition of the water displays a seasonal change, whilst the composition of the former is often a factor of several variables that include not only seasonal variation but also residence time and how the wastewater is managed.

 

On this page, we highlight some of the methods currently being employed for wastewater treatment. It is emphasised that the list is not exhaustive but focused on the methods that have resulted in long-term successful management of wastewater treatment.

Wastewater Treatment Technology

Methods of wastewater treatment

 

On this page, we highlight some of the methods currently being employed for wastewater treatment. It is emphasised that the list is not exhaustive, but focused on the methods that have resulted in long-term successful management of wastewater treatment.

Wastewater Treatment Systems

Leachate and wastewater: Some Basic Facts

Both leachate and wastewater are produced during the treatment of waste material, whether solid waste within landfill sites or sewage from an accumulation of bipedal sentient beings. Whilst systems differ for differing situations, the general approach to the treatment of the organic content of waste matter is similar. Using either aerobic or anaerobic systems, wastewater is treated to remove the active elements.

However, important in the selection of the treatment system selected, it’s critical to analyse all the data about the wastewater, including its source, composition, flow rate and discharge compliance levels.

Organics offers a variety of different types of systems for the treatment of wastewater. Each is available in different ranges to facilitate site-specific requirements.

Ammonia Strippers

Ammonia recovery using heatOne of the principal contaminants that must be recovered in landfill leachate, and in wastewater in general, is ammonia, present in wastewater or in leachate in several forms. Wastewater treatment is therefore essential.

If ammonia is removed or recuperated from leachate or wastewater with a physical process, use can be made of waste heat from landfill gas or on-site engines to heat the water.

Removal can also be facilitated with pH adjustment.

Ammonia stripping and recovery has been shown to be able to treat wastewater flows of highly ammoniated water.

As has been demonstrated by Organics in Hong Kong over the last 20 years, ammonia can be removed from wastewater using heat alone without the addition of substantial quantities of support chemicals, making ammonia available for recovery.

Thermal ammonia stripping has formed the core nitrogen removal process for several wastewater treatment facilities at several landfill sites and anaerobic digesters in the territory. In Hong Kong, however, the primary driver has been to dispose of ammonia, so it has been thermally oxidised. In one case, at an organics food waste processing plant, a thermal ammonia stripper was installed to treat the centrate from an organic waste anaerobic digestion facility rated at 500m3/day (145,000gpd), with a design influent of 3,510mg/l, and a required discharge of <100mg/l.

Sequencing Batch Reactor

A Sequencing Batch Reactor (SBR) is a relatively low technology aeration method comprising a system of one or more tanks, typically GPR, glass-line metal, or concrete in construction.

The process consists of several defined stages: tank filling, aeration, settlement, discharge, and sludge withdrawal.

This is a reliable, proven, and economic solution for treating wastewater derived from municipal solid waste.

The SBR  is a relatively simple process particularly suited to landill applications.  It is especially effective in removing ammonia to very low levels. The SBR needs less supervision and operational presence than other, more complex treatment systems and is often used to ‘polish’ wastewater at the downstream end of the process.

Aeration Lagoons

Lagoon aeration systems are tried and testing solutions for the treatment of urban wastewater. The technology has evolved significantly over the last few decades. Like all water treatment systems, it is important to undertake a study of the best applicable technology.

Diffuser technology or surface aerators, or a combination of both usually provide the optimum choice for lagoon aeration technology.   

Activated Carbon Columns

Activated carbon is used for the removal of AoX, polishing of COD and other selective removal of toxic trace components in leachate.

Activated carbon filtration is a commonly used technology based on the adsorption of contaminants onto the surface of a filter. This method is effective in removing certain organics (such as unwanted taste and odours, micropollutants), chlorine, fluorine or radon from drinking water or wastewater.

However, this technology is not effective in all situations. For example, for microbial contaminants, metals, nitrates, and other inorganic contaminants. The adsorption efficiency depends on the nature of activated carbon used, the water composition, and operating parameters. There are many types of activated carbon filters that can be designed for household, community and industry requirements. Activated carbon filters are relatively easy to install but require energy and skilled labour and can have high costs due to regular replacement of the filter material.

Evaporation

Evaporation offers the possibility of complete wastewater treatment. Essential is the application of a source of heat, whether from using the power of the sun, landfill gas, or waste heat from power generation engines or solar installations.

The level of sophistication of an evaporation plant depends on the duty requirement and the weather. Even if located in hotter parts of the world, leachate can accumulate in landfills to the extent that simply relying on the sun to do the job is more wishful thinking than proactive landfill management.

The type of evaporation system deployed on any treatment plant will rely on a number of factors including the flow rate, the concentration, the composition of the waste to be treated, and the source of the waste. In most cases, an evaporation system, whether by simple solar evaporation of a more sophisticated plant, will be part of integrated leachate and wastewater treatment systems that may include other components such as aeration to assist in the production of micro-droplets thus producing a greater surface area over which evaporation can function.

 

Reverse Osmosis

In wastewater treatment, reverse osmosis is used to apply pressure to overcome osmotic pressure, a colligative property that is driven by chemical potential, a thermodynamic parameter.

Reverse osmosis removes many types of molecules and ions from solution. It also works well with removing bacteria and is used in both industry and potable-water production. In wastewater treatment, it is used to remove contaminants from water that has already been filtered to remove suspended solids.

In use, solute is retained on the pressurised side of the membrane and the pure solvent passes through it. The membrane “selectively” allows smaller component solutions, such as the solvent, to pass freely, while not allowing large molecules or ions through the pores.

When forcing water through a semi-permeable membrane, pressure is applied to the solution, usually by a pump, allowing water and other molecules with low molecular weights (less than about 200 grams per mole) to pass through micro-pores in the membrane.

Most reverse-osmosis installations use a cross-flow to allow the membrane to continually clean itself. As fluid passes through the membrane the rejected species is swept away from the membrane.

Its use in wastewater treatment is extensive, and it is mostly used in the ‘polishing’ phase for potable water. On landfill leachate, the level of success has been questionable as such systems require intensive operation and maintenance to avoid the system from clogging. Filtration prior to the membranes is important to ensure continuous function.

Anaerobic Digestion

There are several different types of digester technology including lagoons which are typically employed when the feedstock is wastewater effluent from agricultural wastewater or animal manure. Using this technology, typical retention time of material is between 30 and 40 days for the biogas to reach full production. A lagoon is a good option when sufficient land is available.

Other technologies such as Continuously Stirred Tank Reactors (CSTR) and Dry Cell Anaerobic Digestion (DCAD) are used when land requirements are limited. CSTR’s are a proven and reliable technology as an alternative to a lagoon based system but are slightly more expensive to build than a lagoon, and require more attention during operation.

Treatment Systems

Leachate and wastewater

Important in the selection of the treatment system selected, it’s critical to analyse all the data about the wastewater, including its source, composition, flow rate and discharge compliance levels.

Organics offers a variety of different types of systems for the treatment of wastewater. Each is available in different ranges to facilitate site-specific requirements.

Ammonia Strippers

Ammonia recovery using heatOne of the principal contaminants that must be recovered in landfill leachate, and in wastewater in general, is ammonia, present in wastewater or in leachate in several forms. Wastewater treatment is therefore essential.

Ammonia stripping and recovery has been shown to be able to treat wastewater flows of highly ammoniated water.

As has been demonstrated by Organics in Hong Kong over the last 20 years, ammonia can be removed from wastewater using heat alone without the addition of substantial quantities of support chemicals, making ammonia available for recovery.

Sequencing Batch Reactor

A Sequencing Batch Reactor (SBR) is a relatively low technology aeration method comprising a system of one or more tanks, typically GPR, glass-line metal, or concrete in construction.

The process consists of several defined stages: tank filling, aeration, settlement, discharge, and sludge withdrawal.

This is a reliable, proven, and economic solution for treating wastewater derived from municipal solid waste.

Aeration Lagoons

Lagoon aeration systems are tried and testing solutions for the treatment of urban wastewater. The technology has evolved significantly over the last few decades. Like all water treatment systems, it is important to undertake a study of the best applicable technology.

Diffuser technology or surface aerators, or a combination of both usually provide the optimum choice for lagoon aeration technology.   

Activated Carbon Columns

Activated carbon is used for the removal of AoX, polishing of COD and other selective removal of toxic trace components in leachate.

Activated carbon filtration is a commonly used technology based on the adsorption of contaminants onto the surface of a filter. This method is effective in removing certain organics (such as unwanted taste and odours, micropollutants), chlorine, fluorine or radon from drinking water or wastewater.

Evaporation

Evaporation offers the possibility of complete wastewater treatment. Essential is the application of a source of heat, whether from using the power of the sun, landfill gas, or waste heat from power generation engines or solar installations.

The level of sophistication of an evaporation plant depends on the duty requirement and the weather. Even if located in hotter parts of the world, leachate can accumulate in landfills to the extent that simply relying on the sun to do the job is more wishful thinking than proactive landfill management.

Reverse Osmosis

In wastewater treatment, reverse osmosis is used to apply pressure to overcome osmotic pressure, a colligative property that is driven by chemical potential, a thermodynamic parameter.

Reverse osmosis removes many types of molecules and ions from solution. It also works well with removing bacteria and is used in both industry and potable-water production. In wastewater treatment, it is used to remove contaminants from water that has already been filtered to remove suspended solids.

In use, solute is retained on the pressurised side of the membrane and the pure solvent passes through it. The membrane “selectively” allows smaller component solutions, such as the solvent, to pass freely, while not allowing large molecules or ions through the pores.

Anaerobic Digestion

There are several different types of digester technology including lagoons which are typically employed when the feedstock is wastewater effluent from agricultural wastewater or animal manure. Using this technology, typical retention time of material is between 30 and 40 days for the biogas to reach full production. A lagoon is a good option when sufficient land is available.

Other technologies such as Continuously Stirred Tank Reactors (CSTR) and Dry Cell Anaerobic Digestion (DCAD) are used when land requirements are limited. CSTR’s are a proven and reliable technology as an alternative to a lagoon based system but are slightly more expensive to build than a lagoon, and require more attention during operation.

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