The presence of contaminants in biowaste is one of the main barriers for their reuse on to land. These contaminants can be trace elements, heavy metals, organic contaminants contained within; pharmaceuticals, personal care products, antimicrobials or surfactants from cleaning products. Looking at what enters the system right from the very beginning helps us to understand where those contaminants arise from. The key to reducing the levels of contaminants present in the biowaste is to manage the source. Consumers at home play a critical role in help to reduce contaminants present in biowaste, thus CIBR researchers need to work closely in partnership with communities.
Consumer behaviours about the type of cleaning, and personal care products is also an important driver for the “quality” of municipal sewage water and sludge. Research was conducted on consumer behaviours about household products head to Up the Pipe: A household products study for more details.
For more information about Up the Pipe contact: Louis.Tremblay@cawthron.org.nz
A common barrier for the land application of biosolids is the high level of metal residues they can contain, principally chromium, copper, nickel and zinc. Metals are often classified as pollutants, but it is important to recognise they are widespread in nature and some are necessary for sustaining life. Metals become pollutants through anthropogenic activities such as mining, that mobilise them in the environment at concentrations that can be toxic and cause damage to exposed ecosystems. Metals are classified under two categories, the essential and non-essential metals. For instance, zinc is an essential element as it is a key component in many enzymes while copper is essential for the normal function of the enzyme cytochrome oxidase. Deficiencies in these elements can be detrimental to health. Cadmium and lead are examples of non-essential metals. However, even essential metals can be toxic at higher concentrations, both copper and zinc levels must be within suitable dietary or soil concentrations to ensure normal growth and reproduction. This is the concept of “window of essentiality” as exposure to high metal concentrations become detrimental to health.
Metals are challenging to manage in biosolids and biosolid amended soils as they are not biodegradable and unless there’s uptake through natural processes, for example uptake into biota, they will remain where they are indefinitely and accumulate with continued inputs. The key to reduce the accumulation of metals in biosolids and the environment is to manage their principal sources. Metals are common components of industrial processes, found in some personal care products, and in foodstuffs. While industrial sources of metals into waste water treatment plants are controlled by Trade Waste regulations and monitoring, this is not the case for domestic sources of metals. A CIBR review document identified leaching of copper and zinc from plumbing materials into domestic water as a significant source of these metals into biosolids in New Zealand. The review referenced studies identifying alloys, such as brass used in tapware and galvanised steel, that have the potential to leach copper and zinc into municipal wastewater, to read the full review on copper and zinc in household plumbing click here. [PDF, 1.8 MB] Plastic piping systems used in conjunction with high quality brass tapware should leach minimal amounts of copper and zinc, whereas lower grade copper piping and brass tapware will leach significantly higher amounts of metals.
To minimise health risk by reducing the exposure to metals in drinking water, the Ministry of Health encourages consumers to flush a small volume (500 mL is recommended) of water from the tap before drawing water for drinking, cooking or oral hygiene. This practise protects the health of humans consuming domestic water, but the metals still end up in the waste stream and ultimately keep accumulating in biosolids. To better manage this source of metal contamination, there is a need to raise awareness about the role of plumbing systems in the contamination of domestic wastewater, and critically, the quality of plumbing materials. The CIBR review recommended that all metallic materials in new plumbing systems should be of a high quality and used only under conditions to which they are suited as an effective way to reduce the leaching of metals and contamination of plumbosolvent waters. This conclusion is confirmed by Ministry of Health recommendations to:
We should all try to reduce the stress we put on our ecosystems and the use of higher quality plumbing materials that contain lower amounts of contaminant metals and are more resistant to corrosion and leaching is a good start.