Effluent Of Activated Sludge Process Research Articles

Effects of Ozone Dose and Contact Time on Ozonation Process Performance for Treatment of High Rate Activated Sludge Process Effluent

ABSTRACT In recent years, there has been an increase in the interest on organic compounds originating from anthropogenic activities. The presence of these micropollutants in waterbodies can be detrimental for the aquatic organisms even at their trace concentrations. Removal of micropollutants from wastewater by conventional treatment methods is quite limited, thereby existing wastewater treatment plants are not capable of removing these micropollutants. This study investigated the removal of 27 micropollutants and conventional pollution parameters by ozonation of the effluent from a pilot-scale high-rate activated sludge system treating municipal wastewater. Different ozone dosages and contact times were tested during the study. Results revealed that 7 out of 27 micropollutants were detected in the effluent. Over 45% chemical oxygen demand (COD) removal and over 65% total suspended solids (TSS) removal were achieved by the ozonation process. Among the various ozone dosage and contact time combinations investigated in the study; 6 mg/L ozone dosage-20 min contact time, and 9 mg/L ozone dosage-10 min contact time alternatives resulted with the best treatment performance in terms of the removal of micropollutants, COD, TSS, and turbidity. A feasibility analysis was conducted to evaluate the best operational conditions from a techno-economic perspective and the results revealed that the unit cost for ozonation process ranged between 0.033 $/m3 and 0.043 $/m3. Additionally, considering the feasibility, 6 mg/L ozone dose – 20 min contact time combination was found as the optimum alternative. Based on the promising results obtained in this study, ozonation can be offered as a polishing step for the effluents of high-rate activated sludge systems for the improving of the effluent quality.

Unwanted mainstream nitritation-denitritation causing massive N2O emissions in a continuous activated sludge process.

Nitrous oxide emissions can contribute significantly to the carbon footprint of municipal wastewater treatment plants even though emissions from conventional nitrogen removal processes are assumed to be moderate. An increased risk for high emissions can occur in connection with process disturbances and nitrite (NO2-) accumulation. This work describes the findings at a large municipal wastewater treatment plant where the levels of NO2- in the activated sludge process effluent were spontaneously and strongly increased on several activated sludge lines which was suspected to be due to shortcut nitrogen removal that stabilized for several months. The high NO2- levels were linked to a dramatic increase in nitrous oxide (N2O) emissions. As much as over 20% of the daily influent nitrogen load was emitted as N2O. These observations indicate that highly increased NO2- levels can occur in conventional activated sludge processes and result in high nitrous oxide emissions. They also raise questions concerning the risk of increased greenhouse gas (GHG) emissions of the nitritation-denitritation processes - although the uncontrolled nature of the event described here must be taken into consideration - and underline the importance of continuous monitoring and control of N2O emissions.

Modification of natural zeolite and its application to advanced recovery of organic matter from an ultra-short-SRT activated sludge process effluent

Natural adsorbent was optimized from four natural adsorption materials (kaolin, bentonite, diatomite, and natural zeolite) through the comparison of their ability to recover organic matter from an ultra-short-sludge-retention-time (ultra-short-SRT) activated sludge process effluent. Natural zeolite was modified by the loading of three types of chemical coagulants (Fe2(SO4)3, Al2(SO4)3, and ZnSO4) and was used for the study of the advanced recovery of organic matter. The results of Brunauer–Emmett–Teller surface area (SBET) measurements, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses showed that natural zeolite was successfully modified, with decrease in the specific surface area of the modified zeolite (MZ), but some metal ions/metal oxides were loaded onto the surface of natural zeolite. Compared with chemical coagulant and natural zeolite, the organic recovery efficiency from the effluent of the MZs improved, and after the optimization process, the organic recovery efficiency of MZ4 (Zeolite:Fe2(SO4)3 = 4:1), MZ9 (Zeolite:Al2(SO4)3 = 4:1), and MZ13 (Zeolite:ZnSO4 = 2:1) reached 72.0%, 67.6%, and 61.2%, respectively. The MZs can allow a significant amount of recovery of soluble chemical oxygen demand (SCOD) from the effluent, with SCOD recovery efficiencies for MZ4, MZ9, and MZ13 of 44.8%, 44.3%, and 39.4%, respectively. The E4/E6, UV253/UV203, and SUVA analyses after the organic recovery experiments indicated that the generation potential of disinfecting byproducts or halogenated products was reduced in the treated effluent by the MZs. The mechanism can be considered in two ways: the coagulation effect of the loaded metal ions/metal oxides and the physical and chemical adsorption effect based on the hydrogen bond and ππ bond between the MZ and organic matter. This study facilitated the application of organic recovery from wastewater and the advanced treatment of effluent.

Investigation of Zinc Oxide Nanoparticles Effects on Removal of Total Coliform Bacteria in Activated Sludge Process Effluent of Municipal Wastewater

Investigation of Zinc Oxide Nanoparticles Effects on Removal of Total Coliform Bacteria in Activated Sludge Process Effluent of Municipal Wastewater

NDMA formation potential removal in treated effluent by UV/H2O2 process

NDMA formation from treated wastewater is one of the concerns in water reuse. This study focused on NDMA formation potential (NDMAFP) removal in wastewater treated effluent by UV/H2O2 technology. A UV/H2O2 system was tested for the removal performance on both organic precursors and NDMAFP. The system consisted of a low pressure ultra-violet (LPUV) with an intensity of 2 mW/cm2 and a H2O2 dosage of 100 ppm. Reaction time was 60 minutes. Two types of wastewater treated effluents were collected: activated sludge process (ASP) effluent and membrane bio-reactor (MBR) effluent. Results showed efficient dissolved organic carbon (DOC) removal (70%). Dissolved organic nitrogen (DON) removal was less efficient (20–30%). Eighty per cent of NDMAFP in ASP effluent was removed within 1 hour. However, no NDMAFP removal was discovered in MBR effluent. This indicated that the effect of the UV/H2O2 system on NDMAFP removal was water specific. A generation of intermediate NDMA precursors was observed in the ASP effluent. Results indicated that sufficient oxidation should be provided to reduce intermediate NDMA precursors and to achieve NDMAFP removal.

Membrane bioreactor for the treatment of voc laden pharmaceutical wastewater: Effect of biological treatment systems on membrane performance

Present study evaluated the effect of effluent from submerged aerated biological filter (SABF) and activated sludge process (ASP) on the performance of membrane bioreactor (MBR). MBR was operated both in external configuration and internal configuration mode. Feeding SABF effluent to MBR resulted in a flux reduction of 2.3% and 12% under external and internal configurations, respectively. Volatile Organic Compound (VOC) removal from SABF effluent by MBR was only 13% in the external configuration mode whereas VOC was completely eliminated in the internal configuration mode. Treatment of effluent from ASP caused significant flux reduction and increase in transmembrane pressure (TMP) in the MBR. For both internal and external membrane configurations, substantial increase in extra cellular polymeric substances (EPS) and suspended solids resulted in higher membrane fouling during the treatment of ASP effluent. VOC removal from ASP effluent by MBR was achieved only while adopting internal configuration mode. Effective treatment of pharmaceutical wastewater, with less impact on membrane performance and reduced VOC emission to the atmosphere, can be achieved by coupling SABF with MBR and adopting internal configuration mode.

Pilot and full scale applications of sulfur-based autotrophic denitrification process for nitrate removal from activated sludge process effluent

Sulfur-based autotrophic denitrification of nitrified activated sludge process effluent was studied in pilot and full scale column bioreactors. Three identical pilot scale column bioreactors packed with varying sulfur/lime-stone ratios (1/1–3/1) were setup in a local wastewater treatment plant and the performances were compared under varying loading conditions for long-term operation. Complete denitrification was obtained in all pilot bioreactors even at nitrate loading of 10 mg NO3−–N/(L.h). When the temperature decreased to 10 °C during the winter time at loading of 18 mg NO3−–N/(L.h), denitrification efficiency decreased to 60–70% and the bioreactor with S/L ratio of 1/1 gave slightly better performance. A full scale sulfur-based autotrophic denitrification process with a S/L ratio of 1/1 was set up for the denitrification of an activated sludge process effluent with a flow rate of 40 m3/d. Almost complete denitrification was attained with a nitrate loading rate of 6.25 mg NO3−–N/(L.h).

Additional Treatment of Wastewater Reduces Endocrine Disruption in Wild Fish—A Comparative Study of Tertiary and Advanced Treatments

Steroid estrogens are thought to be the major cause of feminization (intersex) in wild fish. Widely used wastewater treatment technologies are not effective at removing these contaminants to concentrations thought to be required to protect aquatic wildlife. A number of advanced treatment processes have been proposed to reduce the concentrations of estrogens entering the environment. Before investment is made in such processes, it is imperative that we compare their efficacy in terms of removal of steroid estrogens and their feminizing effects with other treatment options. This study assessed both steroid removal and intersex induction in adult and early life stage fish (roach, Rutilus rutilus). Roach were exposed directly to either secondary (activated sludge process (ASP)), tertiary (sand filtrated (SF)), or advanced (chlorine dioxide (ClO(2)), granular activated charcoal (GAC)) treated effluents for six months. Surprisingly, both the advanced GAC and tertiary SF treatments (but not the ClO(2) treatment) significantly removed the intersex induction associated with the ASP effluent; this was not predicted by the steroid estrogen measurements, which were higher in the tertiary SF than either the GAC or the ClO(2). Therefore our study highlights the importance of using both biological and chemical analysis when assessing new treatment technologies.

Characterizing activated sludge process effluent by particle size distribution, respirometry and modelling

The particle size distribution (PSD) of the effluent from a typical activated sludge process was measured. The relation between the particle size distribution (PSD), residual biomass and conventional suspended solids (SS) and turbidity of a typical activated sludge process effluent was established with the help of laser scattering, oxygen uptake rate (OUR) measurement and the IWA model analysis. The laser scattering technique is capable of measuring particles between 20 nm and 2000 µm. The final effluent also consists of residual biomass which is unsettled in the secondary settling tank (SST) and the amount of this residual biomass was estimated using OUR measurement and IWA model. The final effluent was found to be dominated by the particles of size 1–10 µm, the size range for most of the bacterial cells (Ekama et al. 1997). The results showed that the total number of particles was correlated to the amount of residual biomass. Correlation determining the relation between laser particle size monitoring results and SS/turbidity measurements was also found. The results showed that the particle monitoring was more sensitive than the SS/turbidity measurement and with further development and improved control, it can used for more complex and sensitive data.

Oxidation of natural and synthetic hormones by the horseradish peroxidase enzyme in wastewater

Steroid estrogens, including both natural estrogens (e.g., estrone – E1; 17β-estradiol – E2; and estriol – E3) and synthetic estrogens (e.g., 17α-ethinylestradiol – EE2), are known as endocrine-disrupting compounds. The objective of this research was to evaluate the feasibility of the enzymatic oxidation of estrogens and to optimize this process in municipal wastewater contaminated with steroid estrogens using horseradish peroxidase (HRP) and hydrogen peroxide. An initial HRP activity of 0.02 U ml −1 was sufficient to completely remove EE2 from the synthetic solution, although greater HRP doses (up to 0.06 U ml −1) were required to remove E1, E2 and E3. The optimal molar peroxide-to-substrate ratio was determined to be approximately 0.45. Based on the Michaelis–Menten kinetics, the HRP had an increasing reactivity with E1, E3, E2, and EE2, in increasing order. In real activated sludge process effluent, an HRP dose of 8–10 U ml −1 was required to completely remove all of the studied estrogens, while only 0.032 U ml −1 of HRP was necessary to treat synthetic water containing the same estrogen concentrations.

Case Studies on Biological Treatment of Tannery Effluents in India

This paper presents a comparative assessment of the cost and quality of treatment of tannery wastewater in India by two common effluent treatment plants (CETPs) constructed for two tannery clusters, at Jajmau (Kanpur) and at Unnao in the state of Uttar Pradesh, India. The Jajmau plant is upflow anaerobic sludge blanket (UASB) process-based, while the Unnao plant is activated sludge process (ASP)-based. Investigations indicated that the ASP-based plant was superior in all respects. Total annualized costs, including capital and operation and maintenance costs, for the UASB and ASP plants were Rs. 4.24 million/million liters per day (MLD) and Rs. 3.36 million/MLD, respectively. Land requirements for the two CETPs were 1.4 hectares/MLD and 0.95 hectares/MLD, respectively. Moreover, the treated UASB effluent had higher biochemical and chemical oxygen demand (BOD/COD) and considerable amounts of other undesirable constituents, like chromium (Cr) and sulfide, as compared with the ASP effluent, which had lower BOD/COD and negligible concentration of sulfide and Cr. Sludge production from the UASB-based plant was also higher at 1.4 t/day/MLD, in comparison to the sludge production of 0.8 t/day/MLD for the ASP-based plant. Also, the entire sludge produced in the UASB-based plant was Cr-contaminated and, hence, hazardous, while only a small fraction of the sludge produced in the ASP-based plant was similarly contaminated. The results of this study are at variance with the conventional wisdom of the superiority of anaerobic processes for tannery waste-water treatment in tropical developing countries like India.