Activated Sludge Type Research Articles

Characterization of sludge from the Fez wastewater treatment plant

The Fès wastewater treatment plant is of the activated sludge type. It has been in service since 2014, and receives 155,400 cubic meters per day of domestic wastewater from numerous urban and rural communities: Fès, Ras El Ma, Oulad Tayeb and Ain Chkef. On the one hand, this WWTP generates clean, purified water which is discharged into the receiving environment without any harm to the environment, and on the other, it produces huge quantities of residual sludge, i.e. 5,100 t/year. The aim of this study is to characterize the sludge from the Fez wastewater treatment plant, following sludge treatability tests by monitoring the various analytical parameters. To be able to choose the right technique for the type of sludge to be treated. In our case, for sludge from the Fez wastewater treatment plant, physico-chemical characteristics were carried out for COD, BOD5, TSS, total nitrogen and phosphorus, showing the sludge’s richness in nutrients. The characterization of the sludge from the Fez wastewater treatment plant showed the potential of this product to be valorized.

Eco-efficient Prototype of Wastewater Treatment Plant Applying Clean Development Mechanism Methodologies – Mediterranean Countries

Municipal wastewater treatment is committed reducing greenhouse gases emissions in line with United Nations Framework Convention on Climate Change (UNFCCC) norms in order to preserve Earth's blanket and lower climate acute changes. Greenhouse gases emissions reduction is the avant-garde of municipal wastewater treatment technologies; however, the process requires particular segmentation of all phases to contain the excessive energy required for treatment. Consequently, Energy analysis is endorsed as essential to sustain a thermodynamic equilibrium of the treatment plant with its environment. Decarbonization, denitrification & phosphorus removal urge the exploitation of sustainable energy whether recovered or renewable to engine the treatment facility. This literature values compile the eco-design of wastewater treatment plant with the avant-garde technologies of greenhouse gases emissions reduction, considering environmental aspects at all stages of treatment process, targeting the lowest possible environmental impact throughout the plant life cycle to create a CO₂-free facility prototype. UNFCCC introduced the greenhouse gases emissions definition in wastewater plants as a project design document for the Clean Development Mechanism (CDM) project AM00801 activity. The literature adopted this project and submitted it as a friendly user interface or a Software to model an Eco-efficient management strategy for wastewater treatment plant aerobic activated sludge type with the offset of environmental footprint measures based on decision making analysis, Input-output analysis, benchmarking and energy balance, net negative emissions including environmental declaration assessing the life cycle from costing, management, and sustainability perspectives.

Assessment of quality and potential reuse of wastewater treated with conventional activated sludge

Climate change and the increasing scarcity of water resources have placed the water sector in Morocco at the centre of the public authorities' interests, because of its decisive role in the country's water security and in supporting its development, particularly irrigated agriculture. This has prompted the scientific community and national authorities to move towards an alternative resource to promote the reuse of treated wastewater in irrigation, which could alleviate this water crisis. This study evaluates the performance of the Al-Hoceima city's low-load activated sludge type wastewater treatment plant by analyzing the quality of raw and treated (domestic) wastewater. Indeed, the analysis of the evolution of the pollution parameters between the entry of the station and its exit, shows average reductions of 99% for BOD5, 97% for COD, 96% for TSS, and for the reduction of heavy metals was as follows: Ba < Co < Mn < Pb < Cu < Zn < As < Ni < Cr < Fe < Cd < Hg. Based on the results of the analyses, all of which comply with the discharge standards, Al-Hoceima WWTP is considered a leader in the field of wastewater treatment. A comparison with the recommendations of Morocco and the international community reveals that the results of on-site parameters such as pH, temperature, conductivity and pollution parameters show that the effluent from the Al-Hoceima wastewater treatment plant is within the standard acceptable limit for irrigation.

Bioreactor Simulation with Quadratic Neural Network Model Approximations and Cost Optimization with Markov Decision Process

The efficient operation of activated sludge type wastewater treatment plants is an ongoing topic for the utility providers, where electric energy consumption shares are high, giving cca. 30 % of total operational costs. Intervention methods for intensification include fine tuning of aeration settings, sludge removal and the adjustment of recirculation rates. In order to analyze the effects of various process control strategies, activated sludge models (ASM) are used for the purpose of biokinetic modeling. In practice, most model simulators do not incorporate optimization and necessary auto-calibration of the latter, due to high computational demand of timeseries evaluation. In this paper, a new mathematical model is presented, which makes biokinetic simulations suitable for the use in decision support systems. Namely, the ASM model is approximated with a computanional inexpesive quadratic model solution, fed into a set of mass-balance corrected neural networks. Cost optimization is achieved with Markov decision process model. The developed method was illustrated for a case of Hungarian, large wastewater treatment plant. It was proven, the model is able to find better aeration schemes for the plant in aspect of cost of operation and nitrogen removal efficiency. The model can be used to find cost-optimal policies under arbitrary defined conditions. As a benefit, results can be implemented into industrial logic controllers.

Physicochemical and microbiological quality of the treated wastewater of the Marrakech WWTP for irrigation

The urban district of Marrakech has a wastewater treatment plant of activated sludge type. Water treated by this WTTP is intended for the irrigation of golf courses. Tertiary treatment can extract any undesirable substance not removed by the steps before. The aim of this work is to characterize the physico-chemical and microbiological quality of the treated water and to assess the effectiveness of tertiary treatment. The pH varies between 7.1 and 7.7 which is in the range recommended by both the Moroccan and the USEPA standards. The COD content fluctuates between 24.87 and 52.33 mg O 2 / l, which is below the limit value of 60 mg O 2 / l recommended by the French legislation. Concentrations of BOD 5 range is between 1.1 and 4.21 mg O 2 / l which is widely below the standard of 30 mg O 2 / l recommended by the WHO and USEPA for the reuse of treated wastewater. For the SM, the value of 30 mg / l is the threshold set by both the WHO, USEPA and French law. The values ​​of SM fluctuate between 2.86 and 8.46 mg / l which are perfectly in accordance with the recommended standard. The content of nitrates does not exceed 5 mg N / l is lower than the limit set by WHO and the Moroccan standard of 30 mg N / l. The TP content is between 1,88 and 6,23 mg P / L compared with the range 6-20 mg / l agreed by WHO. The microbiological analysis, including research faecal coliforms show that the values ​​obtained are below standard 200, 250 and 1000 UF / l respectively recommended by the USEPA, the French legislation and concomitantly the Moroccan standard and WHO . However, the parasitology examination especially of nematodes attests their total absence, showing the effectiveness of the tertiary treatment. Finally, the water at the outlet of the WWTP of Marrakech, destinated for irrigation has a physicochemical and microbiological quality compliant for irrigation.

Evaluation of forward osmosis membrane performance and fouling during long-term osmotic membrane bioreactor study

Forward osmosis membrane performance and fouling was studied during 100 days of continuous activated sludge treatment. The purpose of the study was to compare the performance and fouling of commercial cellulose triacetate and newly developed polyamide thin film composite membranes that treated high salinity and low salinity activated sludge from two membrane bioreactors. Water flux, reverse salt flux, and specific reverse salt flux were measured to evaluate the performance of virgin and fouled membranes. Membrane autopsy was used to investigate foulant composition and compare physicochemical membrane properties before and after fouling. The results indicated that both membrane types attained steady-state water flux over 100 days, characterized by an initial decline and subsequent steady-state period. Biofouling and organic fouling caused overall water flux decline, in which foulants were identical between membrane and activated sludge types. Water flux results were similar for the two activated sludge types and demonstrated that FO membrane performance and fouling was independent of total dissolved solids, calcium, and mixed liquor suspended solid concentrations. Lastly, virgin membrane properties (i.e., hydrophilicity and surface roughness) did not contribute substantially to membrane fouling. Cellulose triacetate membranes outperformed thin film composite membranes, with lower fouling propensity, higher water flux, lower reverse salt flux, and lower specific reverse salt flux.

Applying low frequency ultrasound on different biological nitrogen activated sludge types: An analysis of particle size reduction, soluble chemical oxygen demand (SCOD) and ammonia release

Applying low frequency ultrasound could effectively pretreat waste activated sludge (WAS) undergoing anaerobic digestion (AD), because the ultrasound can break up the flocs and cell walls. In this study, we applied ultrasound to three types of biological nitrogen activated sludge in an ice bath. Power densities ranged from 0 to 1.30 W mL−1 and reaction times ranged from 0 to 30 min. The three types of sludge included: short-cut nitrification denitrification sludge (SCND-SBR), complete nitrification denitrification sludge (CND-MUCT), and anaerobic ammonium oxidation sludge (AMX-SHARON). Experiments showed that reductions in average particle size were significantly decreased, due to breakage, at an ultrasonic duration of 10 min with different energy densities. More soluble chemical oxygen demand (SCOD) was detected when the ultrasonic density was higher and the duration was shorter, compared to when the density was lower and the duration was longer. Results suggest that ultrasonic density has a greater impact on the SCOD disintegration degree (DDCOD) as compared to operation time. Soluble proteins (SP) and NH4+N were released during the ultrasound; however, this process does not inhibit the subsequent methanogenic activity during the AD process. The ultrasonic density of 1.04 W mL−1 was the most economic and effective, with the highest efficiency in reducing particle size and releasing SCOD. Therefore, applying ultrasound can accelerate the hydrolysis rate, a rate-limiting factor during AD. This may ultimately reduce treatment construction and operational costs.

Bacterial community analysis of activated sludge: an evaluation of four commonly used DNA extraction methods

The effectiveness of three commercially available direct DNA isolation kits (Mobio, Fast, Qiagen) and one published direct DNA extraction protocol (Bead) for extracting bacterial DNA from different types of activated sludge was investigated and mutually compared. The DNA quantity and purity were determined using real-time PCR targeting the bacterial 16S rDNA gene. Microbial community fingerprints were assessed by automated ribosomal intergenic spacer analysis. The resulting community profiles were analyzed with canonical correspondence analysis. Our results clearly demonstrate that direct DNA extraction methods can significantly influence the DNA quantity, purity, and observed community patterns of microbiota in activated sludge. Fast and Mobio generated high amounts of good quality DNA compared to Bead and Qiagen. Mobio also resulted in the detection of the highest number of species while Fast scored the best in discriminating between the community patterns of different activated sludge types. With respect to the characterization of community profiles, our analyses demonstrated a strong sludge type dependent variability among methods. Taking into account our results, we recommend Fast as the most suitable DNA extraction method for activated sludge samples used for bacterial community studies.

Mitigation of methane emissions from sanitary landfills and sewage treatment plants in Jordan

Mitigation of Greenhouse gases deals with measures to reduce the vulnerability of a certain sector to climate change through minimizing net emissions. In this paper, mitigation scenarios aimed at reducing Jordan methane emissions from sewage treatment plants and sanitary landfill sites were proposed and investigated. In the case of sewage treatment plants, As-Samra plant (the largest in Jordan) was selected for this mitigation study. Two scenarios (I and II) were proposed, the first was to expand the plant by the year 2005 using waste stabilization ponds the current treatment technology, and the second scenario involved switching the treatment technology to activated sludge type when the expansion starts in the year 2005. For sanitary landfills, the proposed mitigation scenario was the construction of two biogas plants, each with a processing capacity of 1,000 tons of solid waste per day at Rusaifeh and Akaider—the two largest landfills in Jordan at the beginning of the year 2005. For As-Samra plant, the cumulative reduction in methane emissions by the year 2030 was calculated to be 49 and 146 Gg under mitigation scenarios I and II, respectively. On the other hand, the biogas plant scenario reduces the methane emissions at each landfill by 28.1 Gg annually. The total emission reduction from both landfills in the life span (25 years) of the biogas plants will be about 1,406 Gg CH4. In addition, this scenario generates electricity at a cost of 4.6 cents per kWh, which is less than the Jordan electric long-run marginal cost of generation at 5.5 cents/kWh. Moreover, annual savings of US$4.65 million will be achieved by the replacement of fuel oil with the generated biogas. The mitigation scenarios presented in this paper include measures that positively contribute to the national development of Jordan in addition to considerable reduction in methane emission.. This forms a win–win situation that favors the adoption of investigated mitigation scenarios by the decision-makers of the waste sector in Jordan.

Evaluation of the STP model: Comparison of modelled and experimental results for ten polycyclic aromatic hydrocarbons (PAHs)

Screening level risk assessment models are used by many countries to assess the treatability of organic chemicals during the sewage treatment process, especially those that are new to commerce. The performance of one such model, the sewage treatment plant model, is evaluated in the current study by comparing model predictions with actual measurement data collected at various stages of a typical full-scale activated sludge type sewage treatment plant. A suite of ten polycyclic aromatic hydrocarbons (PAHs) with widely varying physico–chemical properties were monitored for the comparison. Model predicted removal efficiencies were in very good agreement with those measured for all ten PAHs. Observed chemical concentrations and their trends at various stages of the sewage treatment process were also well simulated by the model. Results also suggest that a reasonable first approximation estimate of a range for the biodegradation half-life needed for the model may be obtained by dividing reported aqueous biodegradation half-life by scaling factors of 50 and 150.

Membrane biological reactor treatment of a saline backwash flow from a recirculating aquaculture system

A recirculating aquaculture system (RAS) can minimize water use, allowing fish production in regions where water is scarce and also placing the waterborne wastes into a concentrated and relatively small volume of effluent. The RAS effluent generated during clarifier backwash is usually small in volume (possibly 0.2–0.5% of the total recirculating flow when microscreen filters are used) but contains high levels of concentrated organic solids and nutrients. When a RAS is operated at high salinities for culture of marine species, recovering the saltwater contained in the backwash effluent could allow for its reuse within the RAS and also reduce salt discharge to the environment. Membrane biological reactors (MBRs) combine activated sludge type treatment with membrane filtration. Therefore, in addition to removing biodegradable organics, suspended solids, and nutrients such as nitrogen and phosphorus, MBRs retain high concentrations of microorganisms and, when operated with membrane pore sizes <1μm, exclude microorganisms from their discharge. In this research, an Enviroquip (Austin, TX) MBR pilot-plant was installed and evaluated over a range of salinities to determine its effectiveness at removing bacteria, turbidity, suspended solids, nitrogen, phosphorus and cBOD5 content from the approximately 22m3/day concentrated biosolids backwash flow discharged from the RASs at The Conservation Fund Freshwater Institute. The MBR system was managed at a hydraulic retention time of 40.8h, a solids retention time of 64±8 days, resulting in a Food: Microorganism ratio of 0.029day−1. Results indicated excellent removal efficiency (%) of TSS (99.65±0.1 to 99.98±0.01) and TVS (99.96±0.01 to 99.99±0.0) at all salinity levels. Similarly, a 3–4log10 removal of total heterotrophic microbes and total coliform was seen at all treatment conditions. Total nitrogen removal efficiency (%) ranged from 91.8±2.9 to 95.5±0.6 at the treatment levels and was consistent, provided a sufficient acclimation period to each new condition was given. Conversely, total phosphorus removal efficiencies (%) at 0ppt, 8ppt, 16ppt and 32ppt salinity were 96.1±1.0, 72.7±3.5, 70.4±2.3, and 65.2±5.4, respectively, indicating reduced phosphorus removal at higher salinities.

What difference might sewage treatment performance make to endocrine disruption in rivers?

An assessment of the steroid estrogen removing performance of 23 different sewage treatment plants (STPs) was performed. The assessment relied on a model to estimate influent concentrations, and completed questionnaires on the STP treatment details from the relevant water companies. This information was compared with observed effluent 17β-estradiol (E2) and estrone (E1) concentrations. The 10 biological filter plants (BFP) in the study performed poorly with only 30% (SD 31) removal on average for E1. This reduced E1 removal performance of the BFPs compared to all the other STP types in the survey was statistically significant ( p < 0.001). Scenarios of all the STPs as activated sludge types, and one as all BFP types were modelled using the GREAT-ER model set up for the Aire/Calder catchment in the UK. This difference was shown to have an important effect on predicted river E1 concentrations and consequent risk classifications.

Simultaneous Carbon and Nitrogen Removal in Anoxic-Aerobic Circulating Fluidized Bed Biological Reactor (CFBBR)

Biological nutrient removal (BNR) in municipal wastewater treatment to remove carbonaceous substrates and nutrients, has recently become increasingly popular worldwide due to increasingly stringent regulations. Biological fluidized bed (BFB) technology, which could be potentially used for BNR, can provide some advantages such as high efficiency and a compact structure. This work shows the results of simultaneous elimination of organic carbon and nitrogen using a circulating fluidized bed biological reactor (CFBBR), which has been developed recently for chemical engineering processes. The CFBBR has two fluidized beds, running as anoxic and aerobic processes to accomplish simultaneous nitrification and denitrification, with continuous liquid recirculation through the anoxic bed and the aerobic bed. Soluble COD concentrations in the effluent ranging from 4 to 20 mg l-1 were obtained at varying COD loading rates; ammonia nitrogen removal efficiencies averaged in excess of 99% at a minimum total hydraulic retention time (HRT) of 2.0 hours over a temperature range of 25 °C to 28 °C. Effluent nitrate nitrogen concentration of less than 5 mg l-1 was achieved by increasing effluent recycle rate. No nitrite accumulation was observed either in the anoxic bed or in the aerobic bed. The system was able to treat grit chamber effluent wastewater at a HRT of 2.0 hours while achieving average effluent BOD, COD, NH3-N, TKN, nitrates, total phosphate, TSS and VSS concentrations of 10 mg l-1, 18 mg l-1, 1.3 mg l-1, 1.5 mg l-1, 7 mg l-1, 2.0 mg l-1, 10 mg l-1 and 8 mg l-1 respectively. The CFBBR appears to be not only an excellent alternative for conventional activated sludge type BNR technologies but also capable of processing much higher loadings that are suitable for industrial applications.

Evaluation of nested PCR–DGGE (denaturing gradient gel electrophoresis) with group-specific 16S rRNA primers for the analysis of bacterial communities from different wastewater treatment plants

The diversity of bacterial groups of activated sludge samples that received wastewater from four different types of industry was investigated by a nested PCR-DGGE (denaturing gradient gel electrophoresis) approach. Specific 16S rRNA primers were chosen for large bacterial groups (Bacteria and alpha-Proteobacteria in particular), which dominate activated sludge communities, as well as for actinomycetes, ammonium oxidisers and methanotrophs (types I and II). In addition primers for the new Acidobacterium kingdom were used to observe their community structure in activated sludge. After this first PCR amplification, a second PCR with bacterial primers yielded 16S rRNA gene fragments that were subsequently separated by DGGE, thus generating 'group-specific DGGE patterns'. The community structure and diversity of the bacterial groups from the different samples was further analysed using different techniques, such as statistical analysis and Shannon diversity index evaluation of the band patterns. By combining the seven DGGE gels, cluster analysis, multidimensional scaling and principal component analysis clearly clustered two of the four activated sludge types separately. It was shown that the combination of molecular and statistical methods can be very useful to differentiate microbial communities.

Evaluation of nested PCR–DGGE (denaturing gradient gel electrophoresis) with group-specific 16S rRNA primers for the analysis of bacterial communities from different wastewater treatment plants

The diversity of bacterial groups of activated sludge samples that received wastewater from four different types of industry was investigated by a nested PCR–DGGE (denaturing gradient gel electrophoresis) approach. Specific 16S rRNA primers were chosen for large bacterial groups (Bacteria and α-Proteobacteria in particular), which dominate activated sludge communities, as well as for actinomycetes, ammonium oxidisers and methanotrophs (types I and II). In addition primers for the new Acidobacterium kingdom were used to observe their community structure in activated sludge. After this first PCR amplification, a second PCR with bacterial primers yielded 16S rRNA gene fragments that were subsequently separated by DGGE, thus generating ‘group-specific DGGE patterns’. The community structure and diversity of the bacterial groups from the different samples was further analysed using different techniques, such as statistical analysis and Shannon diversity index evaluation of the band patterns. By combining the seven DGGE gels, cluster analysis, multidimensional scaling and principal component analysis clearly clustered two of the four activated sludge types separately. It was shown that the combination of molecular and statistical methods can be very useful to differentiate microbial communities.

New approach to oxygen requirement for low-load activated sludge

Low-load activated sludge treatment plants are by far the most numerous and are continuing to develop given their enhanced capacity for nitrogen removal. In general, the electrical consumption of aerators accounts for around 80% of total electrical consumption. It can therefore easily be understood that it is important to be able to evaluate the oxygen requirement for biological treatment as accurately as possible. This evaluation of oxygen requirement is made by the designer during the project phase, using the conventional formula [ O 2 = 1 α (a′Le + b′Xv + c′N) ]. While this approach is entirely satisfactory for the designer (who essentially needs to know the adequate oxygenation capacity), it meets the needs of the operator only imperfectly; the latter needs to know the specific electrical consumption of the aerators as accurately as possible (SEC—kWh.kgBOD −1 5). It is for this reason that an alternative method has been developed allowing calculation of the oxygen requirement for biological treatment (ODCW—kgO 2.kgBOD −1 5) and specific aerator consumption (SEC—kWh.kgBOD −1 5) for low-load activated sludge type plants (Charpentier, 1988). Initially, an ODCW-standard value is obtained, by calculation or from a graph, from the desired concentration in TKN or NH + 4.N for the effluent. ODCW standard = mass of oxygen which the aerators must be able to dissolve in clean water for 1 kg of BOD 5 to be eliminated in “standard” operating conditions. For “non-standard” operating conditions (volumetric load <0.18 kg BOD 5.m −3.d −1; [VSS] aeration ≠ 3 g.l −1; [ TKN BOD 5 ] influent ≠ 0.25 ; [BOD 5] influent > 1000 mg O 2.l −1), the ODCW standard value must be combined with correction factors k 1, k 2, k 3 and k 4 of which the values and conditions of application have been defined:ODCW plant=ODCW standardX k 1 k 2 k 3 k 4 SEC=ODCW plant/SOTR

Evaluation and modification of the simpletreat chemical fate model for activated sludge sewage treatment plants

The SimpleTreat model of Struijs et al. (1991a,b) for chemical fate in a generic activated sludge type wastewater treatment plant (WWTP) has been examined together with an improved model version (vers. 2.1jm) which gives more flexibility in the specification of the WWTP design and operating conditions and which includes a more accurate description of the process of volatilization. Model predictions for 15 different organic chemicals have tentatively been compared with observed removals in three specific Danish WWTP's, all low loaded plants with nitrogen removal. Biodegradation rate constants were either default values for readily or inherently degradable chemicals proposed in the EU Technical Guidance Document on Environmental Risk Assessment of New and Existing Substances (EUTG), or were judged from literature data. The model predictions were generally in fair agreement with the observed removals although exceptions were noted. For 10 chemicals the data allowed estimations of “full scale” biodegradation rate constants by model calibration. Rate constants (extrapolated to 20°C reference temperature) ranged from 0.07 L/(g SS ·d) for pentachlorophenol to 12 L/(g SS ·d) for the every readily degradable compound, p-cresol. Finally, example calculations with parameter values representing a generic Danish WWTP have been compared with example results stated in the EUTG. The predicted emissions in the generic EU WWTP were up to 3-4 times less to water and air and the emission with excess sludge up to 10 times higher than the corresponding figures for an average Danish WWTP.

Evaluation and modification of the simpletreat chemical fate model for activated sludge sewage treatment plants

The SimpleTreat model of Struijs et al. (1991a,b) for chemical fate in a generic activated sludge type wastewater treatment plant (WWTP) has been examined together with an improved model version (vers. 2.1 jm) which gives more flexibility in the specification of the WWTP design and operating conditions and which includes a more accurate description of the process of volatilization. Model predictions for 15 different organic chemicals have tentatively been compared with observed removals in three specific Danish WWTP's, all low loaded plants with nitrogen removal. Biodegradation rate constants were either default values for readily or inherently degradable chemicals proposed in the EU Technical Guidance Document on Environmental Risk Assessment of New and Existing Substances (EUTG), or were judged from literature data. The model predictions were generally in fair agreement with the observed removals although exceptions were noted. For 10 chemicals the data allowed estimations of “full scale” biodegradation rate constants by model calibration. Rate constants (extrapolated to 20°C reference temperature) ranged from 0.07 L/(g SS·d) for pentachlorophenol to 12 L/(g SS·d) for the very readily degradable compound, p-cresol. Finally, example calculations with parameter values representing a generic Danish WWTP have been compared with example results stated in the EUTG. The predicted emissions in the generic EU WWTP were up to 3–4 times less to water and air and the emission with excess sludge up to 10 times higher than the corresponding figures for an average Danish WWTP.

Denitrification kinetics in an activated sludge system

For all water bodies especially for sea, lakes, and ground waters it is very important that nutrient pollution is the least possible (minimal). From municipal and industrial waste waters where considerable amount of nutrients is expected it is possible to remove nutrients with biological treatment. The first step is usually aerobic activated sludge treatment and the second step is combined anaerobic-anoxic-aerobic step in different combinations. A very effective process for nitrogen removal is anoxic activated sludge system. It is very important that in the first aerobic step complete nitrification is achieved. In our laboratory denitrification kinetics was studied. The objective of this study was determination of denitrification velocity and attendance of different parallel phenomena such as nitrite, disappearance of nitrate and nitrite, sulphide formation, etc. Denitrification process was studied in two systems, in closed system (such as in closed reactors for denitrification) and in open systems (such as in open denitrification tanks). We found out that denitrification rate in closed systems was from about 8 to 52 mg/l.h and was dependent on activated sludge type, sludge concentration, and temperature of the system. In open system (such as in an anoxic aeration tank) the rate of denitrification was lower than in closed system; it was from 4 to 15 mg/l.h dependent on activated sludge type, sludge concentration, and temperature of the system. Experiments were carried out in the range of temperature from 20° to 30°C.

Denitrification kinetics in an activated sludge system

For all water bodies especially for sea, lakes, and ground waters it is very important that nutrient pollution is the least possible (minimal). From municipal and industrial waste waters where considerable amount of nutrients is expected it is possible to remove nutrients with biological treatment. The first step is usually aerobic activated sludge treatment and the second step is combined anaerobic-anoxic-aerobic step in different combinations. A very effective process for nitrogen removal is anoxic activated sludge system. It is very important that in the first aerobic step complete nitrification is achieved.In our laboratory denitrification kinetics was studied. The objective of this study was determination of denitrification velocity and attendance of different parallel phenomena such as nitrite, disappearance of nitrate and nitrite, sulphide formation, etc.Denitrification process was studied in two systems, in closed system (such as in closed reactors for denitrification) and in open systems (such as in open denitrification tanks). We found out that denitrification rate in closed systems was from about 8 to 52 mg/l.h and was dependent on activated sludge type, sludge concentration, and temperature of the system. In open system (such as in an anoxic aeration tank) the rate of denitrification was lower than in closed system; it was from 4 to 15 mg/l.h dependent on activated sludge type, sludge concentration, and temperature of the system. Experiments were carried out in the range of temperature from 20° to 30°C.