{"id":4078,"date":"2026-10-12T11:24:00","date_gmt":"2026-10-12T09:24:00","guid":{"rendered":"https:\/\/www.di-camillo.com\/?p=4078"},"modified":"2026-10-12T12:33:34","modified_gmt":"2026-10-12T10:33:34","slug":"car-wash-treatment-plants-regulatory-guide","status":"publish","type":"post","link":"https:\/\/www.di-camillo.com\/en\/car-wash-treatment-plants-regulatory-guide\/","title":{"rendered":"Car wash water treatment plants: treatment technologies, environmental regulations and water recycling"},"content":{"rendered":"

The wastewater from vehicle washing<\/strong> bays contains a complex mixture of organic and inorganic pollutants.<\/strong> Washing bodywork<\/span>, <\/span>chassis and engines removes hydrophobic hydrocarbons<\/span>, <\/span>mineral oils<\/span>, <\/span>sand<\/span>, <\/span>mud<\/span>, <\/span>brake residues<\/span>, <\/span>anionic <\/span>and non<\/span>–<\/span>ionic surfactants from detergents<\/span>, <\/span>as well as traces of heavy metals such as copper<\/span>, <\/span>zinc and nickel<\/span>.\u00a0<\/span><\/p>\n

Managing this wastewater requires structured treatment plants able to reduce the pollutant load before discharge into <\/span>the public sewer<\/span>, <\/span>into surface water or onto the ground<\/span>, <\/span>in full compliance with the regulations in force<\/span>.\u00a0<\/span><\/p>\n

The regulatory framework: Legislative Decree 152\/2006 and discharge requirements\u00a0<\/b><\/h2>\n

The primary legislation for discharges from vehicle washing facilities is Italian Legislative Decree 152\/2006<\/strong> (the <\/span>Consolidated Environmental Act)<\/span>. <\/span>Under the decree<\/span>, <\/span>wash water is not treated as domestic wastewater but falls into the category of industrial wastewater<\/strong><\/span>.\u00a0<\/strong><\/p>\n

Discharges must strictly comply with the concentration limits set out in Table 3 of Annex 5 to Part Three of Legislative Decree 152\/2006<\/strong> for discharge into surface water or the public sewer<\/span>, <\/span>or with the stricter limits of Table 4<\/strong> for discharge onto the ground<\/span>.\u00a0<\/span><\/p>\n

Critical parameters and concentration limits (AUA) <\/b><\/h2>\n\n\n\n\n\n\n\n\n\n
Critical parameter<\/th>\nPublic sewer limit<\/th>\nSurface water limit<\/th>\nNotes and technical meaning<\/th>\n<\/tr>\n<\/thead>\n
Total hydrocarbons (C10-C40)<\/strong><\/td>\n\u2264 10 mg\/l<\/td>\n\u2264 5 mg\/l<\/td>\nPresence of mineral oils and fuels<\/td>\n<\/tr>\n
Total suspended solids (TSS)<\/strong><\/td>\n\u2264 200 mg\/l<\/td>\n\u2264 80 mg\/l<\/td>\nSand, mud and abrasion residues<\/td>\n<\/tr>\n
Total surfactants (MBAS\/BIAS)<\/strong><\/td>\n\u2264 4 mg\/l<\/td>\n\u2264 2 mg\/l<\/td>\nChemical residues from washing detergents<\/td>\n<\/tr>\n
COD (chemical oxygen demand)<\/strong><\/td>\n\u2264 500 mg\/l<\/td>\n\u2264 160 mg\/l<\/td>\nIndicator of the overall organic load<\/td>\n<\/tr>\n
pH<\/strong><\/td>\n5.5 \u2013 9.5<\/td>\n5.5 \u2013 9.5<\/td>\nTo avoid acidification or alkalinisation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Exceeding<\/strong> these thresholds<\/span>, <\/span>whether unintentionally or systematically<\/span>, <\/span>results in administrative and criminal penalties<\/span>, <\/span>as well as suspension of the operating permit<\/span>.\u00a0<\/span><\/p>\n

Stages of the physico<\/b>–<\/b>chemical treatment process\u00a0<\/b><\/h2>\n

A standard car wash treatment<\/a> plant with physico<\/span>–<\/span>chemical or mechanical operation is arranged in several treatment <\/span>sections in series<\/span>.\u00a0<\/span><\/p>\n

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    Grit removal and primary sedimentation\u00a0<\/b><\/h3>\n<\/li>\n<\/ol>\n

    The raw wastewater enters a grit chamber sized to promote gravity settling of the coarser suspended solids (sand<\/span>, <\/span>soil<\/span>, <\/span>grit)<\/span>. <\/span>Calculating the hydraulic retention time is essential to ensure that heavy particles settle on the bottom, preventing the transfer pumps from clogging.\u00a0<\/span><\/p>\n

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      Oil separation with coalescence filter\u00a0<\/b><\/h3>\n<\/li>\n<\/ol>\n

      The de-<\/strong>gritted water passes into the oil separation<\/strong> section for the removal of non<\/span>–<\/span>emulsified hydrocarbons and free oils. To optimise the process, separators fitted with coalescence filters<\/strong> in high specific surface plastic material, such as polyurethane or polypropylene, are used.\u00a0<\/span><\/p>\n

      The filters work by aggregating oil micro<\/span>–<\/span>droplets into larger bubbles, whose buoyancy allows them to rise rapidly to <\/span>the surface<\/span>. <\/span>The surface hydrocarbon layer is then removed by skimmer or overflow baffles<\/span>. <\/span>Oil separators must be <\/span>designed and tested to UNI <\/strong><\/span>EN 858-1 and UNI EN <\/strong>858-2<\/strong>, which define the class of the plant (Class I, with residual oil discharge below 5 mg\/l<\/strong>)<\/span>.\u00a0<\/span><\/p>\n

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        Neutralisation and chemical flocculation\u00a0<\/b><\/h3>\n<\/li>\n<\/ol>\n

        Where strongly alkaline or acid detergents are used in the wash<\/strong><\/span>, <\/span>or where stable oil<\/span>–<\/span>in<\/span>–<\/span>water emulsions are present<\/span>, <\/span>chemical dosing becomes necessary<\/span>. <\/span>Through dosing pumps controlled by measuring probes<\/span>, <\/span>reagents are added <\/span>such as<\/span>:\u00a0<\/span><\/p>\n