Our sludge consistently produces levels of copper that render it unacceptable for spreading purposes.
The weird thing is that there is no local industrial activity such as tree farming or market gardening that could explain it.
Local spring water is not particularly high in the metal, nor is the drinking water supply for the municipality.
Has anyone else experienced this problem? What was the origin?
Actually I did come across this problem for a small town of some 2000 residents. There was no obvious industrial or agricultural source. After a lot of research, it turned out that the physicochemical properties of the local drinking water reacted with the copper piping, thereby releasing it into the water.
If the drinking water supply is aggressive (in terms of calcium carbonate equilibrium), it will tend to attack metal pipes along the network as well as the household pipes of consumers.
Even if domestic pipes are increasingly made of HDPE, there is still a lot of copper piping out there.
I encountered this problem in a town where the levels of copper in the sludge exceeded regulatory limits and precluded its being spread. Using data from a metallographic analysis of individual homes over the previous 10 years, I discovered the weight of the copper generated by the drinking water gave me orders of magnitude similar to the weight of the copper found in the sludge.
The formula looked like this:
[Mean concentration of tap water copper x annual volume consumed] +/-= [concentration of copper in the sludge before spreading x annual volume of sludge generated by the WWTP].
Doing this type of calculation might help you establish whether the source of the copper in the sludge is actually copper from household water systems.