Økologisk byfornyelse og spildevandsrensning, 58 – Udvikling af metode til karakterisering af gråt spildevand

Udvikling af metode til karakterisering af gråt spildevand

Summary and conclusions

Grey wastewater is wastewater produced in kitchens, showers, hand basins and laundry, e.g. wastewater from households without the toilet included. There is an increasing interest for reuse of grey wastewater in the world, however, the arguments for doing that differs. Sustainable development is the major driving force in EU. The limited water resources due to the climate are the major reason for reuse of grey wastewater in countries like USA, Spain, Israel and Australia, while the high pressure on the water resources due to the high population density is the reason in e.g. Japan.

There is generally a need for treatment of the grey wastewater before it can be reused, where the level of treatment is dependent on the way the water is going to be reused. The reason is the presence of different kinds of pollutants (particles, BOD, COD, nutrients, heavy metals, xenobiotic organic compounds and micro-organisms) in the grey wastewater. Pathogenic micro-organisms may constitute a risk to human health for the user of the reuse wastewater, as well as for those who will come in contact with the water during treatment and transport. The presence of nutrients and micro-organisms are of importance for the level of re-growth in installations for water supply as well as in the storage tanks. There is a risk for pollution of soil and receiving waters if the grey wastewater is going to be used for reuse activities outdoors. Reused grey wastewater should also be without any smell and colour, due to esthetical reasons. Consequently, there is a need for knowledge regarding the presence and quantities of chemical compounds and micro-organisms that may constitute a risk or that potentially can cause some kind of problem. Knowledge of the characteristics of the grey wastewater is also needed in order to select the best method for treatment as well as a suitable reuse purpose. Toilet flushing, laundry, irrigation, fire protection, washing of out door areas, infiltration and creation and protection of recreational areas are examples of reuse possibilities.

The overall aims of this project were to collect information regarding the presence and quantities of pollutants in grey wastewater, and to develop a method for characterisation of grey wastewater.

A literature survey showed that the present knowledge regarding the presence and the quantities of pollutants in grey wastewater is restricted to measurements of pH, total alkalinity, SS, organic matter (BOD, COD), nutrients (N, P and K), and heavy metals. There are some studies that have included micro-organisms in their monitoring programs. Studies’ including xenobiotic organic compounds originating from household chemicals and hygiene products are lacking. Information regarding toxicity and health risk related to the individual pollutants as well as the grey wastewater as such, is also limited. Furthermore, knowledge is lacking regarding the quality of the primary grey wastewater types (kitchen, bathroom excl. toilet, laundry), since most studies are focusing on the mixture; classical grey wastewater. Consequently, there is an urgent need for well-defined broad monitoring programs, in order to obtain the information needed regarding the content of chemical compounds and micro-organisms, as well as the toxicity of the grey wastewater.

Most monitoring programs have a number of limitations. They are expensive to carry out, there is lack of analytical methods for analysing many of the potentially present compounds, and it is generally difficult to take representative samples. This is why a methodology for characterisation of grey wastewater has been developed within the present study. The method has two parts a) an inventory and b) measurements. The aim of the inventory is to evaluate the content of pollutants in the grey wastewater, from the behaviour of the people producing the water. The monitoring program is quantitative measurements of the content of pollutants. The methodology was tested on an existing grey wastewater reuse plant in a residence building; BO-90 in Copenhagen.

The present study is the first study that has included xenobiotic organic compounds in the monitoring program, besides the classical monitoring parameters. The study shows that the grey wastewater produced at BO-90, contains pollutants in concentrations within the same concentrations ranges as published from other similar studies in the open literature. The concentrations of the classical wastewater parameters vary as a function of time. A number of extreme values were observed, which results in wide concentration ranges for several of the measured parameters.

Compounds present in household chemicals and other products used in the households, e.g. washing powders, softeners, dishing and cleaning agents, disinfectants and bleaching products, drain cleaners, shampoos, conditioners and skin products, are the dominating source for xenobiotic organic compounds in the grey wastewater. Potentially can 899 different xenobiotic organic compounds be present in grey wastewater, according to the present study. It was not possible to get statistical information regarding neither the quantities of household chemicals used in Denmark, nor the quantities of different compounds in the individual households chemicals.

The inventory performed at BO-90 showed that approximately 70 different household products are used in the bathrooms in the 17 apartments. The dominating products were shampoo, hair conditioner, toothpaste and different skin crèmes. In total 290 compounds was registered in the products that were used. For instance, amyloglucosidase (enzyme), citric acid (softener), cocamidpropylbetaine (amphoteric surfactant), EDTA (softener), glycerine (emulgator), laurylsulphate (anionic surfactant), methyl-, ethyl- and propylparabene (conservation agent) and PEG-7-glycerylcocoate (nonionic surfactant).

In total 201 xenobiotic organic compounds were found in the quantitative measurements of grey wastewater from BO-90. The groups represented were; surfactants (e.g. LAS, nonyl phenol), emulgators (e.g. 1-Hexadecanol, 1-Octadecanol), flavours (e.g. caffeine, camphor, citronellal), conservation agents (e.g. benzoic acid, butylhydroxytoluene, ethylparabene, triclosane), softeners (e.g. bis(2-ethylhexyl)phthalate, dibutylphthalate,), UV-filters (Parasol MCX), solvents (e.g. 2-hexadecanol, ethylbensene, toluene) etc.

There were no positive observations of Salmonella, Campylobacter or Legionella in the samples of untreated, as well as treated and stored grey wastewater from BO-90. This indicates that there are limited risks for infections from these bacteria when grey wastewater is reused. There were, unfortunately no measurements for virus included in the study, since there were no suitable analytical methods available. However, virus may constitute a health risk, depending on the type of grey wastewater as well as the reuse strategy and selected method for treatment.

Finally, the study showed that the results obtained from an inventory will constitute an excellent basis for design of a focused and relevant monitoring program. It became also clear that results from single measurements cannot be extrapolated to grey wastewater in general. Furthermore, the results indicates that pre-treatment will be needed before reuse of grey wastewater in households or for irrigation or groundwater recharge, since the concentrations of pollutants in the grey wastewater are too high.