Characterisation of sludge from street gullies

Abstract

Sludge from street gullies, emanating from stormwater, is often deposited at a landfill for nonhazardous waste. According to EU regulations the amount of waste that goes to landfills
should be minimized, and one purpose with this study was to see if it might be possible to
reuse the sludge in the society instead of deposit it. The sludge was collected from street
gullies in Malmo Municipality (ca 250 000 inhabitants) in Southern Sweden and samples
were taken from one area with low traffic (LT) intensity and one with high traffic (HT)
intensity. According to the regulations the waste should be characterised and the leachability
of the material should be tested. In this study two recommended EU methods for leachability
testing of waste, prEN 14405 and SS-EN 12457-3 were used. A number of parameters were
determined in the sludge as well as in the eluates obtained from the two leaching tests. These
include pH, conductivity, DOC and inorganic ions as e.g. chloride. A number of metals as e.g.
Cd, Cr, Cu, Hg, Ni and Zn, were determined by ICP- MS and organic compounds were
screened by HPLC-DAD and GC-MS. It was found that the concentrations of metals and
organic compounds in the sludge were several orders of magnitudes higher than the actual
eluate concentrations. Our results shown that sludge from street gullies seem to be relatively
harmless. All average values were clearly below the proposed limit values for non-hazardous
waste, except for dissolved organic carbon (DOC) and phenol index (for inert waste) for the
LT sludge. The HT sludge could be re-circulated in the society after the first dewatering step
and the LT sludge could be re-circulated after a treatment step reducing concentrations of
phenolic compounds and DOC.