Effective removal of toxic care products from household grey water

Many areas in the world suffer from a shortage of clean water. The situation is different in the Netherlands, where drinking water is used for applications such as flushing toilets. The reuse of household waste water offers an opportunity to reduce the use of clean water and alleviate the scarcity of water. Household waste water is comprised of the discharge from toilets (black water) and the discharge from showers, washbasins, kitchen sinks and washing machines (grey water). Grey water accounts for some 80% of Dutch household waste water. Grey water is less polluted than black water, which contains substantially higher concentrations of pathogenic microorganisms, hormones and medicine residues. The objective of this project was to develop an effective concept for the treatment of grey water for its safe reuse in non-potable applications. Additional attention was devoted to the removal of personal care products, since some compounds in these products are toxic and, consequently, harmful to the environment.

Care products

The Wageningen researchers made grateful use of a new housing district in Sneek, where 32 homes are equipped with vacuum toilets that separate black water from grey water. Energy is generated from black water and nutrients are recovered, while the grey water is treated ready for reuse. The researchers began by analysing the grey water for the presence of 18 constituents of personal care products. Aromas, UV filters, biocides, preservatives, surfactants and plasticisers were found in very low concentrations. Although these would appear to be innocent, some of these compounds accumulate in animals such as fish and disrupt their hormonal balance.

Biological treatment

The researchers then compared three biological water treatment systems:

• an aerobic (oxygen-rich) treatment in a Sequencing Batch Reactor
  
• an anaerobic (oxygen-free) treatment in an Upflow Sludge Blanket Reactor
  
• a combination of these treatments

Parameters including the reduction of the chemical oxygen demand (COD) were measured to compare the treatments in the appropriate manner. The reduction of the COD is a measure of the quantity of organic pollutants removed from the waste water. Measurements were also carried out to determine the amount of energy each treatment yields in the form of biogas and the amount of waste sludge that is produced. Analyses were carried out to determine whether compounds from personal care products remained in the water after each type of treatment and, if so, the concentrations. The most important finding was that the aerobic system achieved the highest reduction of the COD (90%). No energy is produced by this process. Although the anaerobic system did produce energy, it removed less of the personal care product compounds examined in this study than the aerobic treatment.

Post-treatment

The three biological treatments did not remove all the harmful compounds in personal care products. Consequently, an advanced post-treatment process was required. Two technologies were tested:

• ozonisation
• adsorption on active charcoal

Ozonisation is based on the oxidation and resultant destruction of the remaining personal care product compounds. Adsorption on active charcoal renders the compounds harmless by bonding them on the surface of the charcoal. Both technologies proved highly effective in removing the personal care product compounds examined in the study. A biological treatment in the aerobic system followed by a post-treatment yielded grey water that was highly suited to use in applications such as flushing toilets, washing machines and irrigating agricultural crops.

Links

• Comparison of Three Systems for Biological Greywater Treatment