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Begrænsning af humane medicinrester og antibiotikaresistens i spildevand med fokus på reduktion ved kilden

Summary and conclusions

This study was initiated on behalf of the Minister for the Environment in regard to recent inquiries concerning the risk of discharging pharmaceutical residues with the wastewater including spread of antibiotic-resistant bacteria in the environment. At the same time, an increasing number of municipalities have requested more detailed guidelines regarding assessment and regulation of wastewater from hospitals. The report is the first step towards better regulation and contains an update of the knowledge on pharmaceutical substances in wastewater from hospitals; treatment efficiency and on the potential technologies for pretreatment of wastewater from hospitals. Subsequently, this knowledge is compared in order to identify pharmaceutical substances that potentially can cause effects in the water environment.

The study is based on the Danish pharmaceutical consumption, which was examined in the primary health sector (where prescriptions are given to individuals by a doctor in private practice) as well as in the secondary sector (hospitals). In order to give an overview of the discharge of pharmaceutical products to the wastewater, four cases were set up:

• All of Denmark
• The sewer catchment area to Renseanlæg Lynetten (largest Danish WWTP)
• Frederiksberg Hospital
• Vejle County

Presence and removal of pharmaceutical substances from wastewater

According to the calculations, approx. 1-4% of the whole pharmaceutical consumption takes place at hospitals. However, many pharmaceuticals are only used at hospitals. These hospital specific pharmaceuticals are often very hazardous with respect to the aquatic environment, e.g. special medicine for treatment of cancer, HIV-infections and similar serious diseases. Furthermore, many of these hospital specific pharmaceuticals cannot be quantified, and therefore they do not appear in the tables of this report. This does, however, not exclude them from constituting a potential risk to the environment.

In the report, the following environmentally relevant concentrations are estimated: PEC_hospital, PEC_{inlet WWTP} and PEC_{water environment} (Predicted Environmental Concentration). These three PEC values are related to PNEC (Predicted No-Effect Concentration) for the individual pharmaceuticals in order to examine whether the PEC/PNEC ratio exceeds 1 at discharge from hospitals, at inlet to WWTPs and at outlet from WWTPs (the water environment).

In literature, data on ecotoxicological effects are only available for few pharmaceutical metabolites; hence in order to evaluate whether a pharmaceutical substance has a potentially adverse effect on the water environment, this project was based on a worst-case scenario. The calculations were based on the assumption of 100% excretion of non-metabolized pharmaceutical substances from humans and no removal in municipal treatment plants. Thereby potential pharmaceutical metabolites will be included in the calculations.

Sixteen pharmaceutical substances with a PEC_hospital/PNEC relation of >1 were identified by calculating the total consumption of pharmaceutical substances in Denmark and compare the consumption with the total amount of wastewater, which is 601.8 mill. m³/year. As to PEC_{inlet WWTP}/PNEC, ten substances were identified having PEC/PNEC >1. Finally, calculations showed that the PEC_{water area}/PNEC ratio was >1 for seven pharmaceutical substances. An overview of pharmaceutical substances with PEC/PNEC >1 is given below.

The above table indicates that PEC_{water environment}/PNEC > are generally to be found within the pharmaceutical groups of antibiotics and hormones. Furthermore, the two most frequently used antiphologistics (painkillers) paracetamol and ibuprofen exceed the value.

In Chapter 3, a literature survey was made regarding the capability of advanced treatment plants to remove pharmaceutical substances, including antibiotics. Furthermore, the capability of antibiotics to promote the development of resistant bacteria and to inhibit the processes in the treatment plants was studied. The survey showed that data on removal efficiency of antibiotics vary a lot, e.g. two large EU projects showed a removal degree from the water phase of between 0 and 90%. On this basis it is not possible to demonstrate, which parameters that are crucial in an effective removal of antibiotics. However, a high sludge age (8-10 days) seems to result in the best removal.

The information about removal efficiency from Chapter 3 was compared to the most problematic pharmaceutical groups from Chapter 2. This comparison showed that the groups of sex hormones and antibiotics exceed PEC_{water environment}/PNEC >1. Thus, these groups constitute a potential risk to the environment.

Besides these two groups it cannot be excluded that some of the hospital specific pharmaceuticals with cytotoxic, mutagenic and reproductive abilities can pose a potential environmental risk.

Furthermore the literature shows that worst-case calculations of antibiotics cannot exclude a possible selection pressure neither than an inhibition of the degradation of organic compounds in the treatment plant. At the same time, an antibiotic may affect the activity of the sludge resulting in continuous inhibition.

The consequence of this in relation to a potential selection pressure has not yet been examined.

Technologies for removal of pharmaceutical substances from wastewater from hospitals

The fundamental requirement in the Environmental Protection Act is that polluting industries must limit the pollution as much as possible by using Best Available Technology (BAT). In Chapter 4, focus is on the treatment of wastewater from hospitals including methods, which, to a great extent, are currently used as advanced treatment of municipal wastewater, treatment of wastewater from industries containing specific substances and/or treatment of water resources for drinking water.

The technologies used for treatment of wastewater from hospitals can roughly be divided in the following technologies:

• Mechanical treatment steps
• Biological treatment processes
• Advanced treatment methods (membrane filtration, UV treatment, ozone treatment and Advanced Oxidation Processes (AOP)

In literature, focus is primary on treatment methods in relation to analyzable pharmaceutical substances, which means that knowledge of technological treatment technologies is lacking for many environmentally problematic pharmaceutical substances.

The removal efficiency of pharmaceutical substances from wastewater by precipitation and coagulation/flocculation varies a great deal. Generally, coagulation/flocculation processes are more efficient than primary precipitation. The removal degree of substances as carbamazepin (anti-epileptic substance) and ibuprofen (rheumatism/painkiller) are low whereas in certain cases diclofenac obtains a removal efficiency of up to 77%. The removal efficiency for antibiotics is 28-35%.

As regards nano filtration, the relationship between the membrane pore diameters and the size of molecules of the pharmaceuticals are of great importance for the retention. In addition, the retention is best for non-polar volatile and hydrophobic substances. Properties such as pH and the membrane loading in relation to the substances that has to be retained, also have an affect on the degree of the retention. The pharmaceuticals carbamazepin and ibuprofen, diclofenac, ethinylestradiol and propranolol are retained with more than 90%. Regarding antibiotics, the degree of retention varies greatly – between 44 and 95%.

UV light has primarily been applied to wastewater in order to deactivate micro organisms. Depending on the radiation intensity, up to 99.99% removal (deactivation) of micro organisms can be obtained. The method may be applied in combination with oxidation processes to disinfect and oxidize at the same time.

Ozonation is frequently used for finishing treatment of biologically treated water. As for antibiotics, steroid hormones and painkillers, removal efficiency of between 90 and 99 % can be obtained.

AOP is a promising process to efficiently deactivate pharmaceutical substances. In processes, where both ozone and OH radicals are included, a complete mineralization will not necessarily occur but the substances will lose their original therapeutic effect. As for the other advanced processes, it is important that the concentration of suspended solids in the wastewater to be treated (<4 mg/l) is low in order to limit the consumption of energy.

Best Available Technology at hospitals

In Chapter 5, focus is on BAT (Best Available Technology) in relation to discharges from hospitals including the physical placement of medical wards plus urine separation and substitution of pharmaceuticals. By treatment close to the source, very little space-consuming technologies are needed, e.g. membrane filtration after urine separation. The most relevant biological treatment method is membrane bioreactors (MBR).

All things considered, the sewage systems at Danish hospitals are difficult with respect to collecting or separating the most critical wastewater streams. Some hospitals are old and extended in several phases. Therefore, many hospitals have many connection points to the public sewer system. Others are high-raised blocks, which typically have sewage systems, where all the wastewater is collected in a single or in two discharges. Hospitals with parallel medical treatment centres and outlets, which are bound up with the individual buildings, provide the best opportunities for grouping wastewater streams and individual treatment of the most critical pharmaceutical substances.

Urine separation could be a possibility in relation to treatment of critical water-soluble pharmaceutical substances, which are excreted via urine. The concentration of pharmaceutical substances will be high and the content of suspended solids will be low in separated urine. Ozone treatment and nano filtration are some of the relevant technologies for treatment of fractionated urine.

As to marketing approval of new pharmaceutical products, environmental risk assessment of the substances is required (EU, 2006). In Sweden, they are classifying pharmaceuticals according to environmental characteristics. By categorizing therapeutically identically-working pharmaceutical products with regard to their environmental properties, physicians can chose to prescribe pharmaceuticals less harmful to the environment.

Test of a method for pretreatment of wastewater from hospitals

The reason for choosing coagulation and flocculation as the pretreatment method to be tested was a number of requirements in relation to the possibilities of implementing the technology in connection with discharge from hospitals to the public sewerage system.

The efficiency of selected chemical precipitants was examined with regard to removal of antibiotic-resistant bacteria. Furthermore, the side-effect of the precipitation was illustrated – i.e. to what extent a reduction of selected antibiotics occur. The tests formed the basis of the determination of operating conditions and the identification of possibilities of separating the precipitated material. Subsequently, data were used for a preliminary technical and economical estimation of pre-treatment of wastewater from hospitals.

Laboratory tests with wastewater from Hvidovre Hospital showed that the technology with filtration, coagulation and flocculation may be considered a promising technology for reducing E. coli and enterococcus – with respect to the total amount of bacteria and the amount of resistant bacteria. The reduction of the total amounts of E. coli and enterococcus including resistant bacteria will in all probability be above 95%.

The costs of construction of a plant for treatment of about 35,000 m³/year are estimated to approx. DKK 630,000. Furthermore, there will be expenditure on establishing sludge treatment facilities. The yearly operational costs for a precipitation plant of the above size including costs for sludge handling, which is considerable, are expected to be approx. DKK 630,000 per year.

Filtration of the wastewater through a filter, which corresponds to treatment on a belt filter, led to a reduction of 85% and 33% of the amounts of E. coli and enterococcus, respectively. The reduction of ampicillin-resistant E. coli and erythromycin-resistant enterococcus was 89% and 38%, respectively. Whichever of the three chemical precipitants (one iron-based and two based on aluminium) were used, a removal of bacteria between 89% and 99.99% was obtained. The best result was the removal of total enterococcus and poorest was the removal of ampicillin-resistant E. coli. Among the nine antibiotics analysed before and after precipitation, the best removal efficiency (32 and 91%) were obtained for ampicillin and ciprofloxacin, respectively. Regarding the other antibiotics, no essential removal was obtained.

Conclusions

The literature review about pharmaceuticals in wastewater from hospitals and from the primary health sector resulted in the following conclusions:

• According to the calculations, between 1-4% of the total consumption of pharmaceuticals are used at hospitals.
• Scanty knowledge found about removal of pharmaceuticals in modern treatment plants and with extended nutrient removal, calculations show that among high-volume pharmaceuticals, paracetamol and ibuprofen together with certain antibiotics and sex hormones constitute a risk to the water environment.
• Paracetamol and ibuprofen are well transformed/metabolized in the treatment plants but because of the large load, these substances may in certain cases pass through the plant in concentrations, which make them hazardous to the environment.
• As regards the vast majority of special pharmaceuticals, which are primarily used at hospitals, it cannot be assessed whether they constitute a risk to the water environment due to lack of information about their fate in the treatment plant or their ecotoxicological properties.
• For a number of antibiotics, e.g. tetracycline, amoxicillin, penicillin, roxithromycin, erythromycin and ciprofloxacin, it has been shown that worst-case calculations cannot exclude that some individual antibiotics may either cause a selection pressure or inhibit the transformation of other substances. At the same time, however, it must be stressed that sludge can be adapted to degrade antibiotics. Whether an adaptation influences the selection pressure has not been scientifically examined.
• The number of hospitals is decreasing, whereas the number of hospitalized patients is the same. The concentration of pharmaceuticals in hospital wastewater is expected to increase.
• The number of hospitalized cancer patients is increasing and an increased discharge of cytostatica must be expected.
• The trend is towards fewer but larger and more specialized hospitals. This means that, in future, it should be easier to identify the critical wastewater streams and to establish pretreatment at particularly critical discharges, if necessary.
• AOPs are promising processes for effectively inactivating of pharmaceuticals either at municipal treatment plants or at hospitals. The draw back to the technology is that the concentration of suspended solids has to be low (<4 mg/l) to secure a low energy consumption and efficient treatment.
• At hospitals, urine separation can be used in connection with treatment of critical water-soluble pharmaceuticals, which are excreted via urine. Ozone treatment and nano filtration are among the potentially relevant technologies for treatment of fractionated urine.
• Laboratory tests with hospital wastewater showed that technologies with filtration, coagulation and flocculation should be considered promising technologies to reduce E. coli and enterococcus – the total number of bacteria and the number of resistant bacteria (more than 95% removal).

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Version 1.0 September 2007, © Miljøstyrelsen.