Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: a review.

Microplastics are widely detected in wastewater treatment plants. They can remove microplastics from wastewaters with a high yield, but it means that microplastics are transferred and accumulated to sewage sludge. Lately, increasing attention has been paid to microplastics in raw and treated wastewaters. However, studies about quantification and identification of microplastics in sewage sludge are very scarce and need to be further investigated. Since the sludge-based microplastics are newly studied and are a challenging matrix due to high organic content, there is limited knowledge of sampling, pre-treatment methods, identification techniques, and expression units. Besides, treated sewage sludge is mostly used for soil amendment to improve soil fertility and it gives economic advantages. This situation creates a pathway for microplastics entering the soil environment with unknown consequences. To the best of our knowledge, microplastics have a large specific surface area, small size, and hydrophobicity which makes it a good adsorbent for other pollutants. Therefore, the combined effect of microplastics with adsorbed pollutants such as heavy metals, antibiotics, and persistent organic pollutants could give serious harm to soil safety and soil organisms. Herein, new developments in the methods for sampling, pre-treatment, and identification techniques of microplastics in sewage sludge were reviewed. Then, the abundance of microplastics, major polymer types, and shapes in sewage sludge were examined. Finally, the effects and ecological risks of microplastic pollution as a result of agricultural usage of sewage sludge in the soil environment have been summarized. Also, the main points for future research were highlighted.

Disintegration of biological sludge: Effect of ozone oxidation and ultrasonic treatment on aerobic digestibility.

The present study deals with disintegration of biological sludge by ozone oxidation and ultrasonic treatment. The effects of ozone and ultrasonic treatment were investigated on aerobic sludge bio-processing as comparatively. 9690kJ/kg TS of specific energy and 0.1g O(3)/kg TS were applied to sludge samples preceding aerobic sludge digestion. In terms of sludge stabilization, the highest volatile solids reduction and protein degradation were obtained with ultrasonic treatment. Moreover, digesters fed with disintegrated sludge had higher bacterial activities in terms of oxygen uptake rate (OUR) and volatile suspended solids (VSS)/ suspended solids (SS) ratio than control one during the operation period. In terms of dewatering characteristics of digested sludge, ultrasonic treatment led to increase the sludge's resistance to dewatering. This negative effect was not observed in ozone oxidation. In addition, disintegration processes used in this study did not contribute to an improvement in cake solids on a crown press application.