Prior to metals precipitation, many shops use "pretreatment" processes to affect substances that require special treatment or interfere with subsequent treatments. Common metal complexing compounds which will cause interference are listed in Exhibit 6-8. Some shops combine this step with the precipitation and/or flocculation steps. Exhibit 6-9 (PS 064, PS 116, PS 287) shows several configurations for pretreatment or co-treatment using various chemicals.