Integrated EC and hn-SPEF treatment of slaughterhouse wastewater and iron-sludge valorization in fired bricks: A circular-economy approach

Swine-slaughterhouse wastewater (SSWW) carries high organic load, nutrients and pathogens. This study demonstrates an integrated, near-neutral treatment that couples iron electrocoagulation (EC) with heterogeneous solar photo-electro-Fenton (hn-SPEF) and valorizes the resulting sludge. In semi-continuous EC with Fe plates, removals reached TOC 76 %, COD 83 %, TP 100 %, TN 87 % and TSS >96 %, yielding a clarified effluent that carries catalytic iron. The downstream hn-SPEF step operated at natural pH (similar to 8.4) with no external acid/base or Fe salts; under CPC sunlight and 30 mA cm(-2), TOC and COD decreased to 82 +/- 12 and 78 +/- 4 mg L-1, respectively, with full disinfection (<10(2) CFU 100 mL(-1)). The grid-electricity cost of the integrated train was similar to 2.4 US$ m(-3) (hydraulics-dominated), and only grid electricity is costed; solar input is non-billed. Iron-rich EC sludge (3-11 wt%) was incorporated into fired clay bricks that met mechanical and TCLP criteria for non-load-bearing units, linking treatment with waste-to-resource reuse. This work highlights a practical, chemically lean route for high-strength effluents: EC provides pre-clarification and catalytic Fe carryover; hn-SPEF closes the oxidation gap at neutral pH; and brick valorization advances circular-economy outcomes with competitive operating costs.