Fate of priority hazardous substances during sludge phytoconditioning process

Soares, A.1, Lemos, A.C.F.1, Hubble, J.1, Brigg, J2, Taylor, T.2 and Cartmell, E.1, 1Centre for Water Science, Cranfield University, 2Yorkshire Water Limited


Sludge phyto-conditioning (SPC) is a process by which humus or digested sludge is mixed with a
conditioning material (e.g. green-waste), spread in shallow beds and sown with tetraploid ryegrass.
After 8-10 months of treatment, enhanced treated status (E. coli six log reduction and no
Salmonella species in 2 g of dry solids) is achieved. The fate of organic pollutants was assessed in
sludge treated with the SPC process using ryegrass Lolium multiflorum as the phytoremediation
agent. The experiments were set-up in a green-house with pots containing 0.5 kg dry weight (dw) of
green-waste conditioned humus sludge spiked with organic pollutants: 753 mg/kg dw of
nonylphenol; 50 mg/kg dw of fluoranthene, 126 mg/kg dw of lindane and 16245 mg/kg dw of linear
alkylbenzene sulfonate (LAS).

The maximum pollutant removal rate observed during SPC sludge treatment was 5.0 mg
nonylphenol/kg⋅day, 0.3 mg fluoranthene /kg⋅day, 0.3 mg lindane/kg⋅day and 100.2 mg LAS/kg⋅day
recorded during the initial 126 days of the experiment, corresponding to percent removals of 82%,
61%, 66% and 60% for nonylphenol, fluoranthene, LAS and lindane, respectively. Pathogen
removal, E. coli and Total Coliforms occurred during the first 100 days of incubation from starting
values of 5.3±0.5 Log colony forming units (CFU)/kg dw for E. coli and CFU 9.3±0.5 Log CFU/kg dw
for Total Coliforms to non detectable concentrations. Overall, the SPC treatment has been
demonstrated to be an effective treatment process for sludge stabilisation regarding pathogens and
organic pollutants removal that presented a half-life time of 54 days compared with 106 days on
untreated sludge.

Fluoranthene, LAS, Lindane, Nonylphenol, Priority hazardous substances, Phytoremediation,
Ryegrass, Sewage sludge

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