Guidance

Chemical treatment of waste, including oil: pollution inventory reporting

Updated 29 November 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

If you operate a waste transfer station as a Part A1 installation, you must submit data to the pollution inventory. The Environment Agency will have sent you a notice explaining this with your environmental permit.

The ‘general guidance’ available in the pollution inventory reporting guidance gives information that applies to all business and industries. It explains what the pollution inventory is and how to report.

This guidance gives information specific to the chemical treatment of waste including oil. If you carry out other operations, you may need to refer to other pollution inventory reporting guidance.

Chemical treatment operations you might carry out

This guidance applies primarily to chemical treatment plants with a core neutralisation process. We have given details of activities you might carry out. If these apply to you, we have given considerations you should take when completing your pollution inventory submission.

Chemical treatment processes cover a wide range of unit operations and a wide range of wastes. You should consider if this guidance applies to all your activities.

Composition of wastes

We expect treatment plants to undertake analysis of incoming waste to check suitability for processing. The core waste streams are:

• inorganic acids and alkalis, and their rinse waters
• cleaning, washing, and interceptor wastes from a range of processes

Inorganic species are neutralised and precipitated through the main process. Organic species may travel through the plant into the final sludge or effluent. They may also be evaporated during the exothermic reactions of neutralisation or during sludge pressing.

Certain organic wastes contain ‘hidden’ species relevant to the pollution inventory. For example, lubricating oils contain naphthalene, benzene, toluene, ethylbenzene, xylene, phenols, copper, and nitrogen. These can lead to ammonia and xylene emissions to atmosphere during separation from water, or increased levels in the final site effluent.

You will need to undertake a scoping study to identify materials on the pollution inventory list that are not covered by your effluent monitoring programme but are accepted at your site. The main areas to consider are:

• aqueous wastes containing solvents that may be emitted owing to the heat of the process
• high nitrogen wastes with a potential for ammonia emissions to atmosphere
• occasional inorganic wastes, such as arsenic bearing wastes
• phosphorus containing wastes

For waste you receive infrequently or inconsistently, you might not be required to monitor these regularly. For these, it may be easier to estimate annual emissions from waste intake data rather than to extend the monitoring programme. If in doubt, speak to your local Environment Agency site contact.

Delivery, storage, and transfer of materials

We assume that you accept waste by one or more of these routes:

• tanker
• truck
• pipeline
• ship

It is likely that you generally store the waste prior to treatment either in small containers or tanks. Fugitive and notifiable releases can occur during delivery, storage, and transfer of materials.

In many cases fugitive emissions can result from transfer operations between processes (especially non-pumped systems), leaks from containers, and at pressure or vacuum relief valves.

You must consider fugitive emissions within your pollution inventory return. See the general guidance in the pollution inventory reporting guidance for more information.

Atmospheric emissions from chemical treatment of waste are primarily volatile organic compounds (VOCs), acids, or ammonia wastes.

Washing containers and vehicles occurs at many sites, which results in liquid waste. Most liquid emissions are held on the site base and drain back into the process. If liquid waste from washing activities is removed from your site, you should include this in your pollution inventory submission.

Adjusting and neutralising pH

In this process there can be a violent exothermic reaction with a rapid change in pH. Substances which can be emitted from the reactor tank include:

• carbon dioxide (CO₂)
• hydrogen chloride and hydrochloric acid (HCl)
• nitrogen oxides (NOx)
• sulfur oxides (SOx)
• volatile materials, such as cleaning solvents in wash waters

The gases will carry liquors and particles with them.

In general, reaction tanks are fitted with alkaline scrubber units and most of the acid gases will be returned to the process along with some of the VOCs and almost all the particles and liquors. You should consider if you are releasing any substances during this process.

Small adjustment of pH is a regular part of many chemical processes, or you might do it to modify the final effluent. All intermediates should be retained in the solution with no significant discharges to atmosphere. Any discharges must be included in your pollution inventory submission.

Pre-treatment

There is a wide range of pre-treatment processes that you might carry out. Common ones are:

• oxidation of cyanides
• reduction of hexavalent chromium solutions
• stripping of solvents from aqueous solutions
• gravity separation of soluble oils, and oil and water mixtures

In these processes, the aqueous fraction after pre-treatment normally goes into the main neutralisation process.

You might have atmospheric emissions from pre-treatment. Your processes might:

• have their own atmospheric emission control systems
• be covered by the main plant system
• discharge to atmosphere

In general, we expect that pre-treatment systems for very hazardous wastes will have their own abatement systems.

Areas that may have less stringent abatement systems and may lead to emissions are:

• ammonia emissions from acid cracking of oils
• general VOCs from oil separation
• problems with replacement of filters

Evaporation

Evaporation is usually carried out in fully enclosed systems, but some vent valves can result in fugitive emissions. Your plant should be kept in a satisfactory condition to minimise fugitive emissions.

Evaporation can also occur in an uncontrolled manner. For example, evaporation of solvents from mixing solids and liquids, or the stirring of sludges in open tanks.

Solvent extraction

There is a significant potential for emissions from transfer and emergency releases of solvents. We expect this to normally be well operated and regulated. Many systems return the extraction solvent for reuse in a closed loop.

Once the streams are separated, consider how the supernatant is decanted or separated for subsequent transfer, and the discharge of contaminated product.

Settlement

You are unlikely to experience significant issues with releases from settlement or sedimentation. Emissions to atmosphere are possible but unlikely owing to the quiescence necessary for effective performance.

This is a concentration process so the design of the tanks and residence time will affect the particle size distribution of the final sludge. Hence this will affect the distribution of pollution inventory reportable substances between sludge and the supernatant.

Filtration and pressing

This is a common area for emissions from a chemical plant. The air space above your press might be attached to the main abatement system at the plant, but this is not the case in all sites.

The need to maintain the presses and remove cake or sludge means that the doors are open on a regular basis, making it hard to avoid emissions. Ammonia is the most likely species to be emitted to the atmosphere. Residual VOCs are also commonly released if there is a high organic content in your waste streams.

Emissions relevant to your site

We have provided a list of activities that happen at most treatment sites, and the emissions expected from these activities. The scale of the emission depends on waste throughput and abatement systems at your site. These are the key substances you need to consider for reporting to the pollution inventory, but others may also be released.

• air stripping (designed or in association with general agitation and heating at the plant) – emissions to air include ammonia, VOCs (including organic solvents such as methylene chloride)
• neutralisation – emissions to air include HCl, chlorine, NOx, SOx, ammonia
• neutralisation – emissions to water include chloride, phosphorus, nitrogen, metals
• sludge pressing – emissions to air include ammonia and VOCs
• sludge blending – emissions to air include particulates and VOCs (particularly if this is an exothermic system)
• other material throughput – emissions to water include total organic carbon (TOC), methylene chloride, phenol, benzene, toluene, xylene, ethylbenzene, naphthalene

If you handle biocide contaminated wastes, it is possible that the following substances will be emitted. Otherwise, these can be reported as ‘n/a’ for all relevant media unless you know better for your site:

• aldrin
• atrazine
• brominated diphenylethers
• DDT (dichlorodiphenyltrichloroethane)
• dichlorvos
• dieldrin
• endosulfan
• endrin
• hexachlorobenzene
• hexachlorocyclohexanes
• nonylphenols
• PCBs (poly chlorinated biphenyls)
• pentachlorophenol
• simazine
• tributyltin compounds
• trifluralin

Quantifying emissions to air

Most sites have some abatement equipment to control atmospheric emissions. This varies from extensive systems covering all reaction tanks, storage tanks and sludge pressing areas, to more limited systems covering the main reaction tank alone. The actual atmospheric emissions from individual plants will depend on the abatement system. Very few plants have monitoring programmes in place that can quantify their emissions.

Most of the atmospheric emissions are associated with the transfer and bulking of VOCs and these are the key emissions to quantify. Other waste streams that are known to contribute to emissions are ammonia wastes, strong acid wastes, and powders or dusty wastes.

Several equations are available to calculate emissions from different processes. Check the ‘waste transfer station guidance’ in the pollution inventory reporting guidance notes. It covers the following operations:

• filling bulk storage tanks by road tanker
• gravity and vacuum emptying of drums, IBCs, and other containers to bulk tanks
• storage and handling of empty IBCs, drums, and smaller units

Quantifying emissions to water

Most sites are on a totally enclosed base with all liquids entering or generated on the site (including rainfall) returned to the process. Liquid effluent generally goes to sewer.

Your site permit is likely to have a set of conditions relating to this discharge. The conditions define sampling and monitoring frequency, and the maximum concentration allowed for different species in the effluent. They also define a maximum daily, weekly or monthly quantity of different species. This requires flow proportional monitoring, or the monitoring of each batch before discharge of a set volume. Either system provides the data to calculate annual emissions to the pollution inventory for a number of the main species.

The problems in scoping emissions to water are restricted to those species that are known to exist, but for which there is no monitoring data. It also includes unexpected species that arrive with particular waste streams.

How to quantify emissions from other processes

Check our ‘waste transfer station guidance’ in the pollution inventory reporting guidance notes.

Special issues for oil recovery operations

We have provided lists of substances expected to occur in any plant processing waste lubricating oils, or oil and water mixtures by physical processes. This may include filtering, settlement, and heat treatment to separate oil, water, and solids.

The species come from three main sources:

• original components of the oil
• products from the breakdown of the oil in use
• residues from oil additives

Common emissions to air from oil recovery:

• benzene
• NMVOCs
• PAHs (not generally expected in atmospheric emissions, but possible from processing operations producing a fine mist of oil)
• phenols (possible, but generally not expected due to solubility in oil and water)
• xylenes

Common emissions to water from oil recovery:

• arsenic (As)
• benzene
• cadmium (Cd)
• chloride
• chromium (Cr)
• copper (Cu)
• ethylbenzene
• lead (Pb)
• nickel (Ni)
• nitrogen (total)
• PAHs
• phenols
• phosphorus (total)
• toluene
• total organic carbon (TOC)
• xylenes
• zinc (Zn)

Quantifying oil recovery emissions to air and water

Plants processing only soluble oils or heating oils will have a different range of emissions. For example, most sites take a proportion of lubricating oils.

Plants undertaking acid treatment of soluble oils to break the emulsion may produce ammonia discharges to atmosphere. This is very likely to be below reporting threshold (‘brt’). If you can quantify your ammonia emissions and find them to be below the reporting threshold, you can report either the actual value or write ‘brt’ in the relevant section.

If you undertake distillation processes of specific oils for reuse, such as transformer oils, you will need to make an estimation based on your specific operation.

You are likely to have monitoring data for discharges to sewer of:

• chemical oxygen demand (COD)
• chloride
• nitrogen
• phenol
• some metal species

You might not undertake a wider range of water monitoring or atmospheric emission monitoring. If you do, you can use these data.

Other emissions you may need to consider

This guidance relates to a ‘standard’ oil recovery operation with limited waste streams. Many sites undertake a range of activities and process a wide variety of wastes. You need to check if you are doing additional operations or processing waste types that will add to emissions such as:

• biological treatment prior to discharge to controlled waters to reduce COD, but which emits carbon dioxide to atmosphere
• use of separation facilities for physical treatment or blending with other wastes with, for example, a high COD, metal, or nitrogen content
  • these will provide additional discharges of reportable substances to sewer
  • this could be estimated from intake concentrations and volumes, or by analysis of the sewer discharge
• air stripping columns for high ammonia waste – discharge of ammonia to atmosphere to be calculated by mass balance
• processing of ancillary garage wastes such as degreasing wipes, giving additional VOC emissions to atmosphere
• industrial oils with a known solvent content, or chemical contamination – check if it is on the pollution inventory list and estimate the likely emissions from processing