Summary, Miljøstyrelsen

Reduktion af mineralsk olie i spildevand

Summary

This project investigates how the discharges of mineral oil from small to medium sized enterprises can be reduced through cleaner technology. The project recommends a procedure in which changes in work procedures, substitution of detergents and supplementary treatment technologies are investigated. Moreover, concrete recommendations concerning methods of oil analysis and environmental assessment of detergents are given.

Background

Daily processes such as engine washing, degreasing and the washing of vehicles and material are carried out at auto repair shops, iron and metal works and work sites and result in the conveying of stable emulsified mineral oil to the sewerage system. The oil emulsifies through the use of detergents and high-pressure washing or a combination of the two. The oil is separated very slowly and therefore passes through the established oil separators, both the simple oil separators and the more advanced separators with coalescence filters.

The discharge of mineral oil is generally undesirable. This is due to the fact that mineral oil comprises numerous organic compounds, most of which are not easily degradable and may be hazardous to the environment and health.

Aim and target groups

On the basis of this, the aim of the project was to investigate how the discharge of mineral oil from small to medium sized enterprises - through cleaner technology and treatment - can be reduced. The target group is both enterprises and local authorities, which will typically face the problems encountered in drawing up the wastewater permits. The oil separators' function and design have not been in direct focus as there is already a lot of literature on this subject.

Typical processes

In order to get an overall view of which processes result in the discharge of emulsified oil, the participating local authorities (Albertslund, Hvidovre and Høje Taastrup) carried out a mapping of the processes, which are connected to the oil separators in these three local authorities. The mapping - combined with experience gained from literature - resulted in the focusing of the project on the following six types of processes:

1. High pressure engine treatment and cleaning
2. De-waxing and washing in connection with completion of cars
3. Washing of the under carriage in connection with corrosion protection
4. Auto shop activities/lubrication halls
5. Degreasing in washing machines or baths
6. Washing areas with high pressure cleaning, hot water washing or ordinary hoses

The most common washing areas and auto shop activities

The mapping of the extent of the six processes showed that the washing areas and the auto shop activities/lubrication halls are the predominant processes among the six categories.

Survey of detergents

Twenty-one detergents were selected for investigation. The detergents were chosen so that they covered the most frequently used/most sold products for the above-mentioned six processes. The 21 detergents were tested using an oil separation test and nine of these products, which were included in the work with the projects two example enterprises, were environmentally evaluated according to the ABC method from the Environmental Projection Agency's industrial wastewater guidelines.

Oil separation tests, which simulate discharge through oil separators

Oil separation tests were carried out to test of the detergents' individual properties with discharge to gravimetric oil separators after use. A series of laboratory methods have been developed, which attempt to simulate this discharge. The principle of all these tests is that the detergent is mixed with oil and water and its ability to separate in a water and oil phase is subsequently measured. In this way the detergents' splitting ability is tested. That is to say, whether the detergents' emulisifying effect ceases after a fixed time.

Modified German method

From an assessment of six different laboratory methods it was decided to use a modified German method (DB TL 91881, modified) in this project. The method operates with an oil concentration, which is realistic in relation to wastewater, and uses the analysis of the water phase instead of a visual assessment. The analysis reduces the uncertainty connected with a visual assessment, as the oil is not always visible in the water phase.

Cold degreasing agents with good and poor splitting ability

The testing of cold degreasing agents (which comprises more than 95% petroleum based solvents) showed that certain products - without emulsifiers - can separate after the separation test's 5-minute standing time. Other cold degreasing agents - with emulsifiers - have very poor splitting properties.

Alkaline degreasing agents and shampoos

Testing of alkaline degreasing agents and shampoos shows that none of the tested products showed positive self-splitting properties within the 5-minute standing time. Other investigations of water-based products indicate that the oil separates only after standing times of over 120 minutes.

Large discrepancies with regard to separation tests

Furthermore, the test (DB TL 91881, modified) showed - from a double test of six products - that large discrepancies occur (15-100%) with regard to the results. Also, a comparison between tests carried out in this project and the test results from Keminøglen (DI, 1999) showed considerable discrepancies. This emphasises that large discrepancies can occur between the individual separation tests.

Environmental assessments of detergents

The ABC environmental assessment of detergents from the project's two example enterprises grouped the content substances according to how dangerous they were to the environment, into categories A, B, C and n.a. (not assessed substances). A-substances are undesirable in wastewater as the substances are not easily degradable, are very toxic to organisms living in water and/or can result in incurable harmful effects on humans. Bsubstances should be limited so that the environmental quality requirements are not exceeded, as B-substances are not easily degradable and because they are toxic to organisms living in the water. C-substances are normally unproblematic substances in relation to treatment plants and water areas and n.a.substances are substances, which it has not been possible to assess due to the lack of data. N.a.-substances should be assessed carefully as they could potentially be A or B substances.

Results of environmental assessment

The environmental assessment showed that three out of a total of 25 assessed substances from the detergents were in category A and were thus assessed as being undesirable in the sewerage system. Five substances were assessed as being B-substances and 16 substances were assessed as being C-substances. The A-substances, which are undesirable in the sewerage system, comprise of a quarternary ammonium compound and crude oil distillers. Crude oil distillers are thus grouped as A-substances due to the fact that they are very difficult to degrade and environmental and health issues are involved. The B-substances, which should only be discharged in limited concentrations so that the quality requirements for sludge and water can be maintained, are complex binders and LAS.

Example enterprises

The two example enterprises involved in the project were: Enterprise 1, which sells and custom-designs fork-lift trucks (the oleaginous wastewater arises in connection with the washing and degreasing of the trucks and their accessories (process no. 6)) and Enterprise 2, a car dealership, where washing and de-waxing in connection with the cleaning/preparation of the cars produces wastewater (process no. 2).

Chemical substances not sufficient

At Enterprise 1 the oil distiller's standards of treatment improved from 60 to 99% following the substitution of the detergent used till then. The mean concentration of mineral oil after the oil separator was, however, still high (120 mg/l). This oil is considered to be strongly emulsified and it was therefore recommended that Enterprise 1 should investigate the potential of washing and degreasing the trucks in batches and thus limiting the approx. 1.5 m 3 of wastewater per day.

Existing treatment technology can be made to work by optimising the pretreatment in the oil separation system

Enterprise 2 used four different detergents and the substitution of one detergent did not result in the improved quality of discharge from the car wash. No improvement could really be expected, as the detergent with the lowest self-splitting properties was not substituted due to expectations concerning an inferior washing result. The strategy for Enterprise 2 is now - in cooperation with their chemical supplier - to substitute this inferior product in particular so that the oil separator system can be optimised and can function as an efficient pre-treatment tool for the adsorbtion filter purchased by the company. It is considered that supplementary treatment technology is necessary to obtain an acceptable discharge quality from Enterprise 2.

General procedure for the reduction of oil discharges

Procedure for use in connection with drafting of wastewater permits

Based on the work with the example enterprises and experience gained while working on the project, a general procedure for the reduction of mineral oil and detergents hazardous to the environment in the wastewater has been drawn up. The procedure can be used in cooperation with enterprises and local authorities in connection with the drafting of wastewater permits.

The procedure can be summarized in the following points (there are more detailed descriptions of the individual points in the report):

1. Change in work procedure. First, the possibilities of changing the work procedures with regard to:

avoiding discharge to the sewers

collecting waste

limiting mechanical emulsification

2. Substitution of detergents. Next, the possibilities for substituting detergents by investigating the detergents':

content of A and B substances

ability to separate

3. Treatment technologies. If neither changing the work procedures nor changing detergent can reduce the discharge of mineral oil, it may be necessary to use supplementary treatment technologies.

Specific recommendations

Experience gained while working on the project has resulted in the following specific recommendations in relation to the work concerning the reduction of discharge of oleaginous process wastewater:

Separation tests give only a general indication - concrete investigations are necessary

It is considered that the oil separation test used and the other existing oil separation tests give only a general indication of the detergents' separation ability in connection with discharge using oil separators. There is always a need for concrete investigations of companies' wastewater to show whether it is possible to obtain a satisfactory wastewater quality by extending the standing time alone.

More emphasis on intrinsic properties

When choosing detergents an assessment of the content substances' intrinsic properties hazardous to the environment and health (e.g. the proj-ect's ABC environmental assessment) should always carry more weight than the results of oil separation tests.

Need for clarification concerning separation tests

Both oil separation tests based on visual judgements and tests based on analyses give significant relative deviations. Before general use of oil separation tests there is a need for an explanation of which chemical/ physical properties in detergents result in good separation abilities and whether it is at all possible to obtain such properties for alkaline degreasing substances and shampoos. In consideration of these reservations, the test method (DB TL 91881, modified) from this project can be used as the introductory investigation of the detergents' separation abilities (according to Addendum 3). The test should be carried out using at least three different standing times, e.g. 5, 30 and 120 minutes and double tests and double analyses, which could indicate deviations from the results, should always be carried out.

Self-splitting cold degreasing agents should be recommended with reservations

Certain cold de-greasing agents - products without emulsifiers - showed positive self-splitting properties during the course of the project. However, from an environmental point of view it is dangerous to recommend the use of these petroleum-based degreasing substances. Petroleum distillers are collectively grouped as A-substances and are therefore undesirable in the sewer system. Therefore cold de-greasing agents should only be used when the company can document that the oil distillers are either collected after use or are removed efficiently in the oil separator.

Water-based detergents require a long standing time

The water-based detergents (alkaline degreasing substances and shampoo products) all showed poor self-splitting properties during the five minutes allotted as the standing time for the test in this project. The passage time should, based on experience, be more than 2 hours (preferably more than 24 hours) before the wastewater with water-based detergents separates. The evaluation of whether batch standing is possible should always be carried out using water-based degreasing substances.

Supplementary treatment (or the collecting of washing water) is generally necessary for processes, which lead to the discharge of great quantities of emulsified mineral oil, such as engine washing, de-waxing and the washing of undercarriages.

Possible economical treatment technologies

The cheapest supplementary treatment technologies in the form of adsorption filters are available from production prices of around 40.000 kr (2000 prices) with running costs for changing the filters of around 4.000 - 16.000 kr per year. Alternatively, low-technology batch standing can also be used. The initial expenditure for traditional coalescence filters including oil separator and digging work will be 100.000-160.000 kr depending on the capacity.

Recommendations with regard to analyses for oil/fat

The gravimetric method should only be used for fatty wastewater

The following is recommended:

The gravimetric method according to DS/R 208 cannot be recommended for the analysis of mineral oil in industrial wastewater. The gravimetric method of analysis should only be used for wastewater tests, in which the majority of the extractable compounds consist of fat, e.g. from the food industry.

DS/R 208 for wastewater containing fat

The gravimetric method of analysis DS/R, modified using pentane as the extraction agent, is recommended for the analysis of fatty wastewater. Through this modification the use of tetrachlormethane dictated by DS/R 208, the carcinogenic compound linked to the breaking-down of the ozone layer, is avoided. Using this method the total oil/fat content (extractable compounds) is determined and it is this parameter, which is regulated in relation to the fatty wastewater. The Danish Environmental Agency's recommended limit value for total oil/fat is 50 mg/l.

ISO/DIS 9377-4 for mineral oil (C -C ) Wastewater containing volatile compounds (<C ) Pentane as an extraction agent The need for revision of the suggested limit

For the analysis of mineral oil (C ₁₀-C ₄₀ ) in the wastewater, the GCFID method according to ISO/DIS 9377-4 is recommended. This recommendation is based on, among others, the results of new tests carried out by DHI (September 2000) showing that the gravimetric methods, in which the sample is dehydrated twice, in fact only measure the heavier compounds present in fuel and crude oil and do not include the lighter oil compounds, (< C₁₄), such as petroleum.

Wastewater containing volatile compounds (<C )

If cold degreasing agents are used in industry, or if there are petrol and petroleum spills, all the compounds in mineral oil products, both the volatile compounds and the heavier oils should be controlled. At the present time this is only possible through two separate analysis steps with analysis for mineral oil ISO/DIS 9377-4 (C ₁₀ -C ₄₀ ) and for volatile compounds (<C ₁₀) using GC-FID respectively. It is expected that in the future this will be able to be carried out in just one analysis. The method for this is still at the development stage.

Pentane as an extraction agent The need for revision of the suggested limit

According to ISO/DIS 9377-4 the extraction agent must be a hydrocarbon or a hydrocarbon mixture with a boiling point between 36 and 69�C. Due to this big span in the standard, it is possible to use different agents and thus there is the risk that the results will not be uniform. Pentane should be used as the extraction agent when using ISO/DIS 9377-4. In this way greater uniformity and comparability with oil analyses can be ensured.

In general, analysis results, in which different methods of analysis and different solvents for the extraction have been used, cannot be compared and cannot be attributed the same importance.

The need for revision of the suggested limit

The use of GC-FID methods for the analysis of mineral oil will give higher analysis results than the gravimetric methods, as petrol and petroleum are included. Thus, with the regulating of wastewater containing these compounds, basis cannot be taken directly in the Danish Environmental Agency's suggested limit value of 10 mg/l for mineral oil. This limit is established on the basis of the mineral oil determined using gravimetric methods. There is a need for consultative limit values in this area, which take into account the possible effects of the light compounds in the sewerage system and treatment plants.