Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review.

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

Fate and removal of iodinated X-ray contrast media in membrane bioreactor: Microbial dynamics and effects of different operational parameters.

Iodinated X-ray contrast media (ICM) are mainly used in medical sector, and their presence in environmental waters is a cause of concern as they are capable of forming highly toxic iodinated disinfection byproducts. In the present study, the removal mechanisms of the three ICM- iohexol, iopromide, and iopamidol were elucidated in a lab-scale aerobic membrane bioreactor (MBR). At steady-state operation (solids retention time (SRT)- 70 days, organic loading rate (OLR)- 0.80 KgCOD/m3-day, nitrogen loading rate (NLR)- 0.08 KgNH4-N/m3-day, hydraulic retention time (HRT)- 12 h), the average removal of iohexol and iopromide was found to be 34.9 and 45.2 %, respectively, whereas iopamidol proved to be highly recalcitrant in aerobic conditions of the MBR (removal <10 % in all phases of the MBR operation). Further, through batch kinetic studies and mass balance analysis, it was observed that ICM were primarily biotransformed in the MBR system and biosorption (Kd < 10 L/Kg) was negligible. The biodegradation rate coefficient values (Kbiol) of the ICM were found to be <0.65 L/g-d which indicate that biotransformation rate of ICM was slow. Increased OLR (1.60 KgCOD/m3-day) and reduced SRT (20 days) were found to negatively affect the removal of the ICM. Further, the removal of ICM was found to depend on its initial concentration, and the increment in the ammonium loading (0.16 KgNH4-N/m3-day) did not favor its removal. The dosing of ICM altered the microbial dynamics of the mixed liquor and reduced the microbial diversity and richness. Bdellovibrio, Zoogloea, and bacteria belonging to TM7-3 class, Cryomorphaceae and Hyphomonadaceae families may contribute in ICM biotransformation.

Investigating the biodegradability of iodinated X-ray contrast media in simultaneous nitrification and denitrification system.

The present study investigated the biodegradation of three iodinated X-ray contrast media (ICM), namely, iopamidol, iohexol, and iopromide, in simultaneous nitrification-denitrification (SND) system maintained in a sequencing batch reactor (SBR). The results showed that variable aeration patterns (anoxic-aerobic-anoxic) and micro-aerobic condition were most effective in the biotransformation of ICM while achieving organic carbon and nitrogen removal. The highest removal efficiencies of iopamidol, iohexol, and iopromide were 48.24%, 47.75%, and 57.46%, respectively, in micro-aerobic condition. Iopamidol was highly resistant to biodegradation and possessed the lowest Kbio value, followed by iohexol and iopromide, regardless of operating conditions. The removal of iopamidol and iopromide was affected by the inhibition of nitrifiers. The transformation products after hydroxylation, dehydrogenation, and deiodination of ICM were detected in the treated effluent. Due to the addition of ICM, the abundance of denitrifier genera Rhodobacter and Unclassified Comamonadaceae increased, and the abundance of class TM7-3 decreased. The presence of ICM affected the microbial dynamics, and the diversity of microbes in SND resulted in improving the biodegradability of the compounds.

Effects of pharmaceuticals on membrane bioreactor: Review on membrane fouling mechanisms and fouling control strategies.

Pharmaceuticals have become contaminants of emerging concern due to their toxicity towards aquatic life and pseudo persistent nature in the environment. Membrane bioreactor (MBR) is one such technology that has the potential to act as a barrier against the release of pharmaceuticals into the environment. Fouling is the deposition of the constituents of the mixed liquor on the membrane surface and it limit the world-wide applicability of MBRs. To remove foulant layer, aggressive chemicals and extra cost consideration in terms of energy are required. Extracellular polymeric substances (EPS) and soluble microbial products (SMP) are recognized as principal foulants. Presence of pharmaceuticals has been found to increase the fouling in MBRs. Fouling aggravates in proportion to the concentration of pharmaceuticals. Pharmaceuticals exert chemical stress in microbes, hence forcing them to secrete more EPS/SMP. Pharmaceuticals alter the composition of the foulants and affect microbial metabolism, thereby inflicting direct/indirect effects on fouling. Pharmaceuticals have been found to increase or decrease the size of sludge flocs, however the exact mechanism that govern the floc size change is yet to be understood. Different techniques such as coupling advanced oxidation processes with MBR, adding activated carbon, bioaugmenting MBR with quorum quenching strains have shown to reduce fouling in MBRs treating pharmaceutical wastewater. These fouling mitigation techniques work on reducing the EPS/SMP concentration, thereby alleviating fouling. The present review provides a comprehensive understanding of the effects induced by pharmaceuticals in the activated sludge characteristics and identifying the fouling mechanism. Furthermore, significant knowledge gaps and recent advances in fouling mitigation strategies are discussed. This review has also made an effort to highlight the positive aspect of the foulant layer in retaining pharmaceuticals and antibiotic resistance genes, thereby suggesting a possible delicate trade-off between the flux decline and enhanced removal of pharmaceuticals.

Human health and ecological risk assessment of 98 pharmaceuticals and personal care products (PPCPs) detected in Indian surface and wastewaters.

The release of pharmaceuticals and personal care products (PPCPs) in environmental waters has become an urgent issue due to their pseudo-persistent traits. The present study was undertaken to conduct a screening-level risk assessment of 98 PPCPs, detected in different water matrices (treated wastewater, surface water, and groundwater) of India, for evaluating ecological risk (risk to fish, daphnia, and algae), human health risk, and antimicrobial resistance (AMR) selection risk by following risk quotient (RQ) based methodology. In the present study, 47% of the detected PPCPs in Indian waters were found to exert a possible risk (RQ > 1) to either aquatic species and human health, or cause AMR selection risk. 17 out of 25 antibiotics detected in the environmental waters were found to pose a threat of AMR selection. 11 out of 49 pharmaceuticals were found to exert human health risk from ingesting contaminated surface water, whereas only 2 pharmaceuticals out of 25 were found to exert risk from the intake of groundwater. Very high RQs (>1000) for few pharmaceuticals were obtained, signifying a great potential of the detected PPCPs in causing severe health concern, aquatic toxicity, and AMR spread. Within India, special attention needs to be given to the pharmaceutical hubs, as the environmental waters in these regions were found to be severely contaminated with drug residues resulting in extremely high RQs. The present study will be helpful in prioritizing the detected PPCPs in the environmental waters of India, for which immediate attention and enforceable guidelines are required.

Anoxic-Aerobic-Anoxic sequencing batch reactor for enhanced nitrogen removal.

An anoxic-aerobic-anoxic process was established to achieve simultaneous removal of organic carbon and nitrogen from wastewater in a sequencing batch reactor. The optimum conditions were attained at a DO of 1.5 mg/L with 1 h pre-anoxic and post-anoxic periods. TOC, NH4+-N, and TN removal efficiencies were 98.76 ± 0.95 %, 98.52 ± 0.48 %, and 88.23 ± 0.62 %, respectively, at optimum conditions. Breakpoints in the pH, DO, and ORP curves provided a clear understanding of biochemical reactions happening in the reactor. Inhibition studies showed that 27.69 % of NH4+-N was removed through nitrogen removal pathways such as heterotrophic nitrification or direct conversion, and 20.55 % of TN was removed through aerobic denitrification. Microbial community analysis confirmed the presence of heterotrophic nitrifiers and aerobic denitrifiers. This study highlighted that the varied redox conditions offered by limited aeration would be beneficial for nitrogen removal, thereby reducing the energy usage and operating costs.

Comprehensive review on iodinated X-ray contrast media: Complete fate, occurrence, and formation of disinfection byproducts.

Iodinated contrast media (ICM) are drugs which are used in medical examinations for organ imaging purposes. Wastewater treatment plants (WWTPs) have shown incapability to remove ICM, and as a consequence, ICM and their transformation products (TPs) have been detected in environmental waters. ICM show limited biotransformation and low sorption potential. ICM can act as iodine source and can react with commonly used disinfectants such as chlorine in presence of organic matter to yield iodinated disinfection byproducts (IDBPs) which are more cytotoxic and genotoxic than conventionally known disinfection byproducts (DBPs). Even highly efficient advanced treatment systems have failed to completely mineralize ICM, and TPs that are more toxic than parent ICM are produced. This raises issues regarding the efficacy of existing treatment technologies and serious concern over disinfection of ICM containing waters. Realizing this, the current review aims to capture the attention of scientific community on areas of less focus. The review features in depth knowledge regarding complete environmental fate of ICM along with their existing treatment options.

Occurrence and fate of emerging trace organic chemicals in wastewater plants in Chennai, India.

The presence of pharmaceuticals, hormones, pesticides and industrial contaminants collectively termed as trace organic compounds (TOrCs) in wastewater has been well-documented in USA, Europe, China and other regions. However, data from India, the second most populous country in the world is severely lacking. This study investigated the occurrence and concentrations of twenty-two indicator TOrCs at three wastewater treatment plants (WWTPs) in South India serving diverse communities across three sampling campaigns. Samples were collected after each WWTP treatment unit and removal efficiencies for TOrCs were determined. Eleven TOrCs were detected in every sample from every location at all sites, while only five TOrCs were detected consistently in effluent samples. Caffeine was present at greatest concentration in the influent of all three plants with average concentrations ranging between 56 and 65µg/L. In contrast, the x-ray contrast media pharmaceutical, iohexol, was the highest detected compound on average in the effluent at all three WWTPs (2.1-8.7µg/L). TOrCs were not completely removed in the WWTPs with removal efficiencies being compound specific and most of the attenuation being attributed to the biological treatment processes. Caffeine and triclocarban were well removed (>80%), while other compounds were poorly removed (acesulfame, sucralose, iohexol) or maybe even formed (carbamazepine) within the WWTPs. The effluent composition of the 22 TOrCs were similar within the three WWTPs but quite different to those seen in the US, indicating the importance of region-specific monitoring. Diurnal trends indicated that variability is compound specific but trended within certain classes of compounds (artificial sweeteners, and pharmaceuticals). The data collected on TOrCs from this study can be used as a baseline to identify potential remediation and regulatory strategies in this understudied region of India.