Microplastics (MPs) have been recognised as an emerging contaminant that may have a direct adverse impact on aquatic organisms as well as humans. In California, the State Water Board will be introducing provisions to monitor MPs in drinking water from 1 July 2021 and one of the areas of concern is MPs entering the water system through the application of biosolids to agricultural land and the potential to impact levels found in drinking water. Sewage filter cake samples were collected and analysed using an LDIR (Laser Direct Infrared) imaging system where the identification of plastics such as polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), polyamide (PA), polymethylene methacrylate (PMMA), and polyacrylic esters was undertaken. Sample digestion using wet peroxide oxidation on the dried filter cake samples is necessary before analysis by LDIR that obtains an IR spectrum in the fingerprint region 975 - 1800 cm-1 and measures the size of the MPs in the 20-500 µm range with particles >500 µm <5 mm via an ATR accessory. A total of 16 filter cake samples were analysed and all contained MPs with PE being the most abundant across the different size fractions. This study will discuss the quality assurance measures implemented to ensure blanks levels were monitored to minimise their impact on the results as well as the use of certified reference materials. An overview of the LDIR imaging technique will be discussed and the results of the filter cake samples will be presented.