Full-scale Activated Sludge Treatment Research Articles

Behavior of Micropollutants in Polishing Units that Combine Sorption and Biodegradation Mechanisms to Improve the Quality of Activated Sludge Effluent

The current study evaluated the removal of six micropollutants (estrone (E1); 17β-estradiol (E2); 17α-ethynylestradiol (EE2); ibuprofen (IBP), diclofenac (DCF), and paracetamol (PCT)) from the final effluent of an activated sludge domestic sewage treatment plant using polishing filters. Four polishing filters were assembled as columns and filled with a mixture of sand and vermiculite, sand and charcoal, sand and granulated activated carbon (9:1 by volume), and sand only. The column filters were placed near the outlet of a full-scale activated sludge treatment plant and were fed with a treated effluent containing from 4.71 to 28.93 ng L-1 of the target compounds at a hydraulic loading rate (HLR) of 50 m3 m−2 day−1. Samples were collected periodically from the influent (biologically treated sewage) and effluent of the four columns and analyzed for estrogens, anti-inflammatories, and analgesic compounds. Liquid samples were submitted to a solid phase extraction (SPE) and analyzed by gas chromatography coupled with mass spectrometry after their derivatization. Among the compounds found, diclofenac was distinguished by the high occurrence of detection in the samples (85%) and higher mean concentration (~ 17 ng L−1). High removal efficiency (> 90%) of the estrogens was observed in the polishing systems studied, while for the other targets, the removal efficiency varied from 10 to 30%. The concentration values of some compounds were low, probably due to rainfall during the sampling period.

Removal of tetracyclines from swine manure at full-scale activated sludge treatment plants

The purpose of this study was to investigate the fate of three tetracyclines (TCs), namely oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC) at two different full-scale swine manure-activated sludge treatment plants. Throughout treatment, OTC, CTC and DC were removed by 71–76%, 75–80% and 95%, respectively. Removal of these TCs under physical treatment was deniable. On the contrary, the flocculation–coagulation and the secondary clarification resulted in a relevant reduction of the concentration of these TCs.

Microbial diversity differences within aerobic granular sludge and activated sludge flocs

In this study, we investigated during 400days the microbial community variations as observed from 16S DNA gene DGGE banding patterns from an aerobic granular sludge pilot plant as well as the from a full-scale activated sludge treatment plant in Epe, the Netherlands. Both plants obtained the same wastewater and had the same relative hydraulic variations and run stable over time. For the total bacterial population, a similarity analysis was conducted showing that the community composition of both sludge types was very dissimilar. Despite this difference, general bacterial population of both systems had on average comparable species richness, entropy, and evenness, suggesting that different bacteria were sharing the same functionality. Moreover, multi-dimensional scaling analysis revealed that the microbial populations of the flocculent sludge system moved closely around the initial population, whereas the bacterial population in the aerobic granular sludge moved away from its initial population representing a permanent change. In addition, the ammonium-oxidizing community of both sludge systems was studied in detail showing more unevenness than the general bacterial community. Nitrosomonas was the dominant AOB in flocculent sludge, whereas in granular sludge, Nitrosomonas and Nitrosospira were present in equal amounts. A correlation analysis of process data and microbial data from DGGE gels showed that the microbial diversity shift in ammonium-oxidizing bacteria clearly correlated with fluctuations in temperature.

Mechanisms of N 2O production in biological wastewater treatment under nitrifying and denitrifying conditions

Nitrous oxide (N 2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N 2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions. Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N 2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N 2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N 2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N 2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N 2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO 2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment. Under anoxic conditions, nitrate reducing experiments confirmed that N 2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N 2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.

Biogas desulphurization at technical scale by lithotrophic denitrification: Integration of sulphide and nitrogen removal

Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m 3 using aerobically treated wastewater containing activated sludge and mixture of nitrate (NO 3 −) and nitrite (NO 2 −) as electron acceptors in industrial relevant conditions. Both nitrate and nitrite were provided from full-scale activated sludge treatment plant operated and controlled using dissolved oxygen and redox sensors to make sure nitrification performed and biogas was provided from anaerobic digester. The biogas flowrate changed from 5 to 25 m 3/h and wastewater flowrate from 2.5 to 15 m 3/h. The volumetric sulphide loading rates ranged between 2 and 22 kg S 2− m −3 d −1. The optimum wastewater/biogas ratio observed for maximum H 2S removal rates was in the range of 2–3 m 3/m 3 and minimum empty bed residence time (EBRT) determined was around 10 min. Nitrogen removal in the form of nitrate and nitrite was found to be proportional to sulphide removal. The redox potential of the effluent was also monitored and related to the wastewater/biogas ratio. More than 95% of H 2S has been removed from biogas in this study when the volumetric sulphide loading rates were between 2 and 4 kg S 2− m −3 d −1. This work reveals that sulphide removal can successfully be integrated to biological nitrogen removal (BNR) in industrial wastewater treatment systems.

Dynamics in Flocculation and Settling Properties Studied at a Full-Scale Activated Sludge Plant

A comprehensive study of the dynamics in settling and flocculation properties at a full-scale activated sludge treatment plant with secondary settlers operated at their maximum capacity is presented. An extensive set of process data was analyzed to assess physical parameters affecting the capacity and performance of the secondary settlers. There was a large variation in the settling and compaction properties, and they changed quickly, as a result of the short sludge age. Even though the flocculation properties changed throughout the year, they were generally improved during the summer, with lower values of effluent turbidity and effluent suspended solids concentration. The shear sensitivity, which is a measure of floc stability, was higher during the winter, when the water temperatures were lower. The sludge floc morphology had, in general, a different internal structure, with more round microbial colonies during the warmer summer months and a more net-like open structure during the winter.

Biological Nutrient Removal of Nitrogen Using Cyclic Aeration: Application in a Full-Scale Activated Sludge Treatment Plant

Biological Nutrient Removal of Nitrogen Using Cyclic Aeration: Application in a Full-Scale Activated Sludge Treatment Plant

Application of quantitative RT-PCR to determine the distribution of Microthrix parvicella in full-scale activated sludge treatment systems

Three wastewater treatment plants in South Africa were investigated to understand the phylogeny and distribution of Microthrix parvicella using real-time polymerase chain reaction (RT-PCR). The phylogenetic analysis of the 16S rRNA of M. parvicella revealed 98% to 100% homology of South African clones to M. parvicella reported in Genbank. The standard curves for RT-PCR showed R2 values greater than 0.99, accurate for quantification. The relative occurrence of M. parvicella 16S rRNA gene copies in the three wastewater treatment plants was in the range 0% to 3.97%. M. parvicella copies increased when the environmental temperature (< or =20 degrees C) and food/microorganism (F/M) ratio was low. The M. parvicella 16S rRNA copies could be positively correlated to the sludge volume index at low temperature. At higher temperature, there was a rapid reduction in M. parvicella population irrespective of other favorable factors, indicating the strong influence of temperature on filamentous proliferation. RT-PCR has potential applications in wastewater treatment plants to monitor sudden shift in the microbial population and assessing the plants efficacy.

Aerobic vs. Anaerobic-Aerobic Biotreatment: Paper Mill Wastewater

The operation of existing activated sludge treatment plants at paper mills in the world is often characterized by disturbances, caused by bad biosolids settling, sludge bulking, and reduction of biomass activity. This paper presents a comparison between the results obtained in a case study based on a full-scale activated sludge treatment (AST) system working as the only biotreatment and the AST working with anaerobic pretreatment by upflow anaerobic sludge blanket (UASB). The study was performed at paper mills in Hedera, Israel. The data was collected during 8 years. The anaerobic/aerobic system (2002–2004) provided steady operation performance, while the AST system without anaerobic pretreatment (1997–2001) produced effluent characterized by oscillatory values. The results indicate much lower levels of total suspended solids in the anaerobic/aerobic treatment system effluent, 5–10 mg/L, compared to 50–85 mg/L in the AST system only. Similar improvement was observed in terms of the organic matter removal: 220–250 mg/L vs. 80–120 mg/L as CODt, and 20–40 mg/L vs. 4–7 mg/L as BODt with low corresponding fluctuations. After the operation of the anaerobic pretreatment, the sludge age increased from 8–10 days to 30–40 days and the activated sludge performance substantially improved: the sludge volume index decreased from 200 to 80 mL/g with significant reduction of the excess sludge amount. The data collected during the operation monitoring clearly indicates that the anaerobic process followed by AST considerably reduced electrical and chemicals consumption in the biological treatment plant and provided low operational cost.

Rain events and their effect on effluent quality studied at a full scale activated sludge treatment plant

The effect of rain events on effluent quality dynamics was studied at a full scale activated sludge wastewater treatment plant which has a process solution incorporating pre-denitrification in activated sludge with post-nitrification in trickling filters. The incoming wastewater flow varies significantly due to a combined sewer system. Changed flow conditions have an impact on the whole treatment process since the recirculation to the trickling filters is set by the hydraulic limitations of the secondary settlers. Apart from causing different hydraulic conditions in the plant, increased flow due to rain or snow-melting, changes the properties of the incoming wastewater which affects process performance and effluent quality, especially the particle removal efficiency. A comprehensive set of on-line and laboratory data were collected and analysed to assess the impact of rain events on the plant performance.

Influence of flocculation and settling properties of activated sludge in relation to secondary settler performance

Floc characteristics were studied at a full scale activated sludge treatment plant with a unique process solution incorporating pre-denitrification with post-nitrification in nitrifying trickling filters. Since greater nitrogen removal is achieved when more secondary settled wastewater is recirculated to the trickling filters, the secondary settlers are always operated close to their maximal capacity. The flocculation and settling properties are therefore crucial and have an effect on the overall plant performance. Since the plant is operated at a short sludge age, these properties change quickly, resulting in variable maximal secondary settler capacity. The dynamics in floc structure and microbial community composition were studied and correlated to the secondary settler performance. Fluorescence in situ hybridisation was used to investigate the microbial community structure and their spatial distribution. The floc structure could to some extent be related to the flocculation and settling properties of the sludge. Even small differences had an influence suggesting that colloidal properties also play a significant role in determining the floc properties. No correlation between microbial community composition and settling properties could be established with the group-specific probes investigated.

Determination of the Fractal Dimension of Microbial Flocs from the Change in Their Size Distribution after Breakage

The fractal dimension is of ultimate importance in the description of the properties and behavior of microbial flocs in biological wastewater treatment systems. However, the methods for the measurement of the fractal dimension have not been well-established. In this study, a new method is developed to determine the fractal dimension of biological flocs in activated sludge (AS) suspensions. The new method utilizes the particle size distribution (PSD) of the sludge flocs measured by image processing under a microscope. Mechanical breakage is conducted for the sludge sample to create a change in the PSD. On the basis of the self-similarity of fractal aggregates, the fractal dimension of the AS flocs can be calculated from a comparison between the original PSD and the altered PSD by breakage. It is determined that the sludge flocs grown in laboratory bioreactors with sludge ages of 5, 10, and 20 days have fractal dimensions of 2.07, 2.21, and 2.36. The sludge collected from a full-scale AS treatment plant has a fractal dimension of 1.99. This new method overcomes the deficiencies of other existing methods. It is easier to use and provides more reliable results in the determination of the fractal dimension of biological flocs and other similar aggregate samples.

Does the semi-continuous activated sludge (SCAS) test predict removal in secondary treatment?

The semi-continuous activated sludge (SCAS) test was formalized by the U.S. Soap and Detergent Association in 1965. The SCAS procedure has also been adopted by the Organization for Economic Cooperation and Development (OECD) as a test for inherent biodegradability and by the U.S. EPA as a test guideline (40CFR 835.3120) under the Toxic Substances Control Act. To investigate whether the SCAS test may be used to predict removal in full-scale activated sludge treatment systems, we first collected all available SCAS data for organic chemicals, and then retrieved data from full-, pilot- or bench-scale continuous-feed activated sludge (CAS) studies for the chemicals that had SCAS data. The intersected file was subjected to statistical analysis. Conclusions were as follows: (i) SCAS data were strongly clustered at high (> 90 %) removal; (ii) for SCAS removal > 90 %, it is probable that removal in the field will be > 50 %; (iii) however, for SCAS removal < 90 % adequate treatability cannot be predicted with confidence.

Chemical characterization and biotreatability of effluents from an integrated alkaline-peroxide mechanical pulping/machine finish coated (APMP/MFC) paper mill

As part of an extensive audit of the Alkaline-Peroxide Mechanical Pulping (APMPTM) plant at the Malette Quebec Inc. mill in St. Raymond, Que., effluents were sampled from various stages of the process for comprehensive chemical characterizations, aquatic toxicity testing and anaerobic biotreatability assessments. In addition, untreated and secondary treated combined effluent from the integrated paper mill were sampled to determine the effectiveness of a conventional activated sludge process at the mill site. During the one-day sampling period, the APMP plant processed a mixed wood furnish consisting of 50% spruce/balsam fir and 50% aspen, with a chemical charge of 3.5% sodium hydroxide and 3.8% hydrogen peroxide on oven-dry fibre, while the Machine Finish Coated (MFC) paper production rate was 100 odt/d (oven dry metric tonnes per day). Measured production-specific contaminant discharge loadings from the novel APMP process were 56 kg BOD5/odt and 155 kg COD/odt in a combined effluent flow of 28 m3/odt. Sources of process effluent were chip washing, three stages of wood chip pretreatment and chemical impregnation (i.e., Impressafiner stages), interstate washing and pulp cleaning. The three Impressafiner pressates were found to be the most concentrated (i.e., 12-26 g COD/L) and toxic streams. Microtox testing of the pressates revealed EC50 concentrations of 0.07-0.34% v/v. The warm and concentrated effluents generated by the non-sulphur APMP process were found to be highly amenable to anaerobic degradation as determined by batch bioassay testing. Filterable BOD5 and COD(f) of the process effluents were reduced by 87-95% and 70-77%, respectively, with corresponding theoretical methane yields being attained. Acid-soluble dissolved lignin compounds exhibited biorecalcitrance, as revealed by limited removals of 34-55%, and were the main constituents contributing to residual COD(f), while resin and fatty acids (RFA) were reduced by 80-94%. The conservatively operated full scale activated sludge treatment process achieved a similar high 74% COD(f) removal from the whole mill effluent, while BOD5 and RFA reductions were virtually complete and the treated effluent was non-toxic, as measured by Microtox.

Chemical characterization and biotreatability of effluents from an integrated alkaline peroxide mechanical pulping/machine finish coated (APMP/MFC) paper mill

As part of an extensive audit of the Alkaline-Peroxide Mechanical Pulping (APMP™) plant at the Malette Quebec Inc. mill in St. Raymond, Que., effluents were sampled from various stages of the process for comprehensive chemical characterizations, aquatic toxicity testing and anaerobic biotreatability assessments. In addition, untreated and secondary treated combined effluent from the integrated paper mill were sampled to determine the effectiveness of a conventional activated sludge process at the mill site. During the one-day sampling period, the APMP plant processed a mixed wood furnish consisting of 50% spruce/balsam fir and 50% aspen, with a chemical charge of 3.5% sodium hydroxide and 3.8% hydrogen peroxide on oven-dry fibre, while the Machine Finish Coated (MFC) paper production rate was 100 odt/d (oven dry metric tonnes per day).Measured production-specific contaminant discharge loadings from the novel APMP process were 56 kg BOD5/odt and 155 kg COD/odt in a combined effluent flow of 28 m3/odt. Sources of process effluent were chip washing, three stages of wood chip pretreatment and chemical impregnation (i.e., Impressafiner stages), interstage washing and pulp cleaning. The three Impressafiner pressates were found to be the most concentrated (i.e., 12–26 g COD/L) and toxic streams. Microtox testing of the pressates revealed EC50 concentrations of 0.07–0.34% v/v. The warm and concentrated effluents generated by the non-sulphur APMP process were found to be highly amenable to anaerobic degradation as determined by batch bioassay testing. Filterable BOD5 and COD(f) of the process effluents were reduced by 87–95% and 70–77%, respectively, with corresponding theoretical methane yields being attained. Acid-soluble dissolved lignin compounds exhibited biorecalcitrance, as revealed by limited removals of 34–55%, and were the main constituents contributing to residual COD(f), while resin and fatty acids (RFA) were reduced by 80–94%. The conservatively operated full scale activated sludge treatment process achieved a similar high 74% COD(f) removal from the whole mill effluent, while BOD5 and RFA reductions were virtually complete and the treated effluent was non-toxic, as measured by Microtox.

On-Line stBOD Measurement and Toxicity Control of Wastewaters with a Respirographic Biosensor

This paper presents the results of the implementation of an on-line respirographic biosensor- RODTOX - for both BOD monitoring and toxicity control of incoming wastewater towards a full scale activated sludge treatment plant. The results showed that this on-line respirometer provided reliable BOD measurements. At two occasions the apparatus detected incoming toxicity and concomitant with these alarms a deterioration of the plant performance effectively occurred. Its reliability for toxicity detection has further been checked by deliberate intoxication experiments with creoline. The results showed that the RODTOX gave toxicity alarm in time so that preventive measures (interruption of the entrance of toxic wastewater) could be taken.

Nitrogen Transformation in Activated Sludge Treatment

In a full-scale activated sludge treatment plant treating nutrient deficient pulp mill waste, the supply of supplementary nitrogen was interrupted for a period of 25 days. This interruption in nutrient supply had very little influence on the treatment efficiency but subsequently when the nutrient addition was recommenced some activated sludge was lost in the effluent and the sludge volume index increased. In this system, nitrification was completely inhibited and the only forms of nitrogen present in the system were ammonia and organic nitrogen. The concentration of ammonia in the final effluent was practically constant and independent of the addition of supplementary nitrogen. The explanation of this is that ammonia released from cellular materials occurs in proportion to the rate of endogenous respiration of the activated sludge.

Chemical Neutralization of Alkaline Wastewater During Activated Sludge Treatment

Abstract The chemical neutralization of alkaline wastewater during the activated sludge treatment is due mostly to the development of CO2 during such biological treatment. The full-scale activated sludge treatment of alkaline wastewater without preliminary separate chemical neutralization was studied for the case of an unbleached Kraft pulp mill effluent. The treatment was carried out in limited-mixing aeration tanks at conventional loadings. Maximum pH values of the mixed liquor were 10.2, and the corresponding total alkalinity values reached 23.8 me/l. It was observed that considerable parts of the waste-water alkalinity were removed during the initial periods of mixed liquor aeration. The practical limit of this type of neutralization seems to be close to pH of 8.

Variation in the activated sludge volume index

From the operational experience of the full-scale activated sludge treatment of the effluent from the unbleached Kraft pulp production in the Ostrołȩka Mill, it was observed that substantial decreases in sludge volume index take place due to the extended storage of the activated sludge in the secondary clarifiers. Moreover, was found that in the studied range of wastewater pH and alkalinity the sludge loadings are the main factor determining the sludge volume index in the aeration tanks. Both decreases and increases of the sludge loading causes increases of the sludge volume index. The optimal sludge load values for the minimal sludge volume index are between 0·3–0·5 g BOD/g of sludge per day. During the mixed liquor piston-type flow in the aeration tanks, at low average sludge loadings, there were also observed increases of the sludge index value and then partial decreases. At higher average sludge loadings the sludge index values after initial minimal decreases showed a tendency to increase.