Compost liquor was treated using a combination of physico-chemical processes: (i) lime precipitation, (ii) filtration on a rotary drum vacuum precoat filter, (iii) ultrafiltration, and (iv) reverse osmosis. Laboratory Jar tests showed the interest of using lime to precipitate compost liquor. Yields of ammonium removal up to 90% were obtained for an optimum lime concentration of 6 g/ L. A test was run at semi-industrial scale on 400 L of highly loaded compost liquor (COD: 15,800 mg/L, ammoniacal pollution: 18,433 mg NH4+-N/L, conductivity: 74,000 μS/cm) to demonstrate the potential of the treatment process proposed. Outstanding purification yields were obtained, especially 95% of COD removal and 93% of ammoniacal pollution removal.