Electrokinetic remediation of fish farm sludge

Abstract

Norway’s fish farming industry generates large amounts of sludge waste that can pollute seafloors and over-enrich the waters if badly managed. The sludge is nutrient rich, but is often exported with minimal processing, missing opportunities for resource recovery. Rising environmental awareness has increased the interest in sustainable sludge management to treat waste as a resource rather than a liability. In this context, electrokinetic remediation (EKR) is being explored as a method to mobilize nutrients for reuse.

Laboratory experiments applied constant voltages of 10V, 20V, and 30V across samples of rehydrated dry sludge and wet sludge in an electrokinetic cell for four days. After each run, X-ray fluorescence (XRF) and X-ray diffraction (XRD) tracked elemental composition and mineral phases to see the effects. pH, electrical conductivity, total dissolved solids, and total/volatile/fixed solids were analyzed prior to electrokinetic remediation.

Voltage strongly affected performance. 20V yielded the most ion movement, 10V was too weak, and 30V led to many ions precipitating instead of migrating. Lighter ions like potassium and calcium migrated freely, but heavier metals like zinc, copper and lead remained largely immobile, likely precipitating near the cathode.

However, the study had several limitations. The sludge samples were not completely untreated as all samples had gone through some treatment, the setup had minor leaks, and each run lasted only four days. These factors likely limited heavy metal migration and removal.

Overall, the results show that EKR can mobilize and transport nutrients, but it is less effective at extracting heavy metals. Further improvements, such as longer treatment, pH control, or combinations of different methods, are recommended. With refinement, EKR could become a useful tool for sustainable aquaculture sludge management.