Multivariate analysis of activated sludge community in full-scale wastewater treatment plants

Recent approaches and advanced wastewater treatment technologies for mitigating emerging microplastics contamination - A critical review

Microplastics have been identified as an emerging pollutant due to their irrefutable prevalence in air, soil, and particularly, the aquatic ecosystem. Wastewater treatment plants (WWTPs) are seen as the last line of defense which creates a barrier between microplastics and the environment. These microplastics are discharged in large quantities into aquatic bodies due to their insufficient containment during water treatment. As a result, WWTPs are regarded as point sources of microplastics release into the environment. Assessing the prevalence and behavior of microplastics in WWTPs is therefore critical for their control. The removal efficiency of microplastics was 65 %, 0.2-14 %, and 0.2-2 % after the successful primary, secondary and tertiary treatment phases in WWTPs. In this review, other than conventional treatment methods, advanced treatment methods have also been discussed. For the removal of microplastics in the size range 20-190 μm, advanced treatment methods like membrane bioreactors, rapid sand filtration, electrocoagulation and photocatalytic degradation was found to be effective and these methods helps in increasing the removal efficiency to >99 %. Bioremediation based approaches has found that sea grasses, lugworm and blue mussels has the ability to mitigate microplastics by acting as a natural trap to the microplastics pollutants and could act as candidate species for possible incorporation in WWTPs. Also, there is a need for controlling the use and unchecked release of microplastics into the environment through laws and regulations.

Biological Activated Sludge from Wastewater Treatment Plant before and during the COVID-19 Pandemic

The COVID-19 pandemic and the related measures brought a change in daily life that affected the characteristics of the municipal wastewater and further, of the biological activated sludge. The activated sludge process is the most widely used biological wastewater treatment process in developed areas. In this paper, we aim to show the situation of specific investigations concerning the variation of the physicochemical parameters and biological composition of the activated sludge from one conventional wastewater treatment plant from a metropolitan area. The investigations were carried out for three years: 2019, 2020 and 2021. The results showed the most representative taxa of microorganisms: Microtrix, Aspidisca cicada, Vorticella convallaria, Ciliata free of the unknown and Epistylis and Rotifers. Even if other microorganisms were found in the sludge flocs, their small presence did not influence in any way the quality of the activated sludge and of the wastewater treatment process. That is why we conclude that protozoa (especially Flagellates and Ciliates) and rotifers were the most important. Together with the values and variation of the physicochemical parameters, they indicated a good, healthy, and stable activated sludge, along with an efficient purifying treatment process, no matter the loading conditions.

Application of Integrated Fixed-Film Activated Sludge in a Conventional Wastewater Treatment Plant

It is often only at the operation stage of a wastewater treatment plant that there is a need to adjust the treatment process in terms of variable hydraulic capacity, increased pollutant load, high/low concentration of suspended biomass, or the unfavorable phenomenon of reduced sedimentation capacity of the activated sludge. One of the ways to improve the treatment process efficiency is to increase the biologically active surface by using bio-carriers in the form of fibers, materials, or bio-balls. This paper presents the results of a wastewater treatment plant operation during the period of six months after the implementation of the integrated fixed-film activated sludge (IFAS) technology. The research showed that microorganisms developed both in the activated sludge and on the fibers, positively influencing the activated sludge condition. During the start-up of the IFAS process, ciliates predominated over the other species. However, as oxygen content was high (2 mg/dm3 and more) and textile beds were used, the protozoan population developed intensively, and small metazoans became increasingly common. Throughout the research period, nitrifying and phosphorus-accumulating bacteria were observed both in the activated sludge and on the fibers. Between the 59th and 184th day of operation, numerous microorganisms were detected on the fibers and in the activated sludge, testifying to low biological oxygen demand, good aerobic conditions for nitrification, and long sludge age. However, the process seemed to break down after day 72, when the occurrence of metazoan led to reduced sludge production; after day 88, chemical oxygen demand and total suspended solids in the outflow increased, and oligochaetes and rotifers dominated the suspended sludge and fibers. Results also showed that the textile bed and low ammonia concentration became an excellent substrate for the development of Stentor sp. With regard to chemical and biological oxygen demand, total nitrogen- and total phosphorus-effluent concentrations were mostly within the legally permissible limits throughout the 184 days of operation.