Aeration Cycle Research Articles

Nutrients removal in overloaded WWTP by intermittently aerated IFAS: Effects of biofilm carrier and intermittent aeration cycle

Updating of the current Urban Waste Water Treatment Directive (91/271/EEC) will demand stricter regulations for nutrients removal. In this frame, wastewater treatment plants (WWTPs) of small-to-medium potential will face new challenges for achieving process intensification. Integrating intermittent aeration (IA) and integrated fixed-film activated sludge (IFAS) technologies could be a promising solution to meet such requirements. This study analyzed how IA cycles affected nutrients removal in IFAS reactors with different biofilm carriers (e.g., plastic and sponge media). The plants responses to different carbon/nitrogen/phosphorous (C/N/P) ratios were evaluated while operating under low sludge retention time (SRT) to simulate overloaded conditions.A short IA cycle (1 h) with an aeration/not aeration ratio of 2:1 enabled high organic carbon and nitrification performances when operating at high C/N/P (11.8/1/1), whereas low denitrification and phosphorous removal yields were obtained because of the short not-aerated phase. Decreasing C/N ratio (8.8/1/1) without changing the IA cycle resulted in nitrification worsening because of the reduced metabolic kinetics of biofilm. Under such load conditions, a higher IA cycle (2 h) was necessary to improve process performance. A longer not-aerated phase was also positive for denitrification and phosphorous removal because of the establishment of anoxic and anaerobic environments within the bulk and inner biofilm layers. Besides, results suggested that sponge carriers offered advantages over plastic ones, enabling a higher biofilm retention capacity, better nutrient removal, as well as robustness and resilience to operating condition changes. This would result in simpler management systems for implementing the IA process, thus reducing process complexity and costs.

Effective nitrogen removal from onsite wastewater using a sequencing aerated biofilm reactor

A novel sequencing aerated biofilm reactor (SABR) was designed for effective nitrogen removal from onsite wastewater with a footprint 10 times smaller than conventional drainfield and a high hydraulic capacity. The study examined the effect of aeration pattern, wastewater strength, and carrier type on N-removal performance. Over 93 % COD removal and > 80 % TN-removal was achieved in the SABR integrated with a polishing unit (10 % woodchips, v/v) at the optimized aeration pattern (4-h pre-anoxic, 7 aeration cycles of 20 min aeration per hour at 1 L-air/min airflow rate, 1 h post-anoxic). Carriers' shape and surface area did not impact SABR's N-removal performance (31.8 % vs. 28.2 %). The optimal operation conditions obtained in bench-scale SABR tests were pilot tested with the 10 % woodchip polishing unit. Efficient TN-removal (72.4 %) was achieved with low effluent TN concentrations (6.5 ± 3.9 mg-N/L) by the pilot SABR. Ammonium (NH4+) was the predominant N-species (5.5 ± 6.0 mg-N/L) in the final effluent while NOx− was constantly below the detection limit (< 0.05 mg-N/L). Quantitative PCR analysis of functional genes involved in N-removal (amoA-AOA, amoA-AOB, nirS, nirK and nosZ) were comparable for bench-scale and pilot-scale SABRs and revealed higher abundance of amoA-AOB (> 4 orders of magnitudes higher than amoA-AOA) and nirS (nirK/nirS: 0.2–1.8 × 10−2), suggesting amoA-AOB and nirS may serve as biomarkers to monitor the system performance. Collectively, the results suggest that SABR offers a versatile approach to treat wastewater at various strengths and is applicable in areas with space constraints, shallow groundwater, and sensitive water bodies.

Activity of Ammonium-Oxidizing Bacteria—An Essential Parameter for Model-Based N2O Mitigation Control Strategies for Biofilms

The reduction in N2O emissions is an important task in the control of wastewater treatment plants. Since local operating conditions, especially inside biofilms, are usually not known, models are an important tool in the development and implementation of control strategies. For a pilot-scale nitrifying biofilm reactor and an SBR, different operational strategies to reduce autotrophic nitrous oxide (N2O) formation were developed and tested by applying a combination of modeling and measurement. Both approaches highlighted the relevance of addressing the actual AOB activity as a sensitive control variable. The investigated strategies, therefore, focused on decreasing the AOB-related NH4 conversion rate, as autotrophic N2O formation is directly linked to AOB activity. The results showed that the biofilm system was more advantageous compared with suspended sludge systems. A higher AOB content resulted in a decrease in AOB activity, leading to fewer N2O emissions at the same reactor performance. The highest reduction in autotrophic N2O formation (SBR: 25%; Biofilm: 27%) was obtained by maximizing the aerated time per day and minimizing the number of aeration cycles (the suppression of nitrite-oxidizing bacteria still needed to be ensured). A higher biofilm thickness or a higher sludge mass in the SBR, however, did not have a noteworthy positive effect since no additional biomass could be kept in the system in the long term due to limited substrate availability. Besides nitritation, denitrification was also identified as a relevant source of N2O in both systems (biofilm: main source) due to the inhibition of N2O reduction by nitrous acid (elevated nitrite concentrations in combination with pH values &lt; 7).

Impact of aeration on/off duration on the performance of an intermittently aerated MBR treating real textile wastewater

Uncontrolled discharge of textile industry wastewater, defined by its highly toxic content, causes serious problems in receiving environment. Especially nitrogen-derived pollutants in wastewater threaten the ecosystem and aquatic life. Separate or simultaneous nitrification/denitrification is the preferred biological processes for removing nitrogen-based pollutants from wastewater. This study aimed to evaluate the impact of aeration on/off cycle durations on organic matter, color, and nitrogen removal performances in an intermittently aerated membrane bioreactor (MBR) receiving real textile wastewater. For this purpose, the MBR was operated under different dissolved oxygen concentrations (6 and 3 mg/L) and the aeration on/off cycle durations (from 2 min/2 min to 90 min/360 min) at a constant flux of 10 L/(m2.h). While the chemical oxygen demand (COD) removal performance ranged from 84 to 91 %, the color removal efficiencies were highly variable. Nitrification performance of ≥89 % was achieved with a minimum of 30 min aeration cycles. The highest denitrification efficiency was obtained in the cycle with 360 min aeration-off duration. Intermittent aeration provided higher TN removal, less sludge generation, and lower energy requirements for aeration. The impacts of aeration cycle duration on membrane filtration performance and foulant characterization were also investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), gel-permeation chromatography (GPC), SEM coupled with energy dispersive spectroscopy (SEM-EDS), particle size distribution (PSD) analyses.

Low-cost ceramic filter bioreactor for treatment and reuse of residential septic tank effluent: A decentralized approach for small communities

Membrane biological reactors (MBRs) have recently become widely accepted as an advanced technology for treating domestic wastewater for improved water recovery, reuse, and recycling. The present study investigated the application of a low-cost ceramic filter bioreactor (CFBR) to treat septic tank effluent for smaller communities in Saudi Arabia (KSA). Filter fouling behavior, pollutant removal, and effluent quality were assessed under varying flux (0.2, 0.4, and 0.65 m/d) and aeration on/off cycle (60 min/60 min, 40 min/80 min, 30 min/90 min, 24 h/24 h) conditions. Operating CFBR at a flux value of 0.4 m/d ensured moderate fouling propensity, reasonable flux decline, and a higher volume of treated effluent. In the continuous aeration mode experiments, CFBR demonstrated the removal of various pollutants. Except for NO3N, CFBR effectively reduced all other pollutants of concern (BOD, COD, TSS, NH3N) in the effluent to acceptable levels meeting the water quality standards for unrestricted irrigation set by the KSA. An enhanced NO3N removal at the 24 h/24 h on/off cycle, indicating the effectiveness of cyclic aeration for promoting both nitrification/denitrification in the CFBR, with sufficient removal of other pollutants, is an original finding of the present study. Simple and cost-effective operations, high-quality effluent, and reduced energy consumption with shorter aeration duration promote the sustainability of the CFBR system for wastewater reclamation and reuse in small communities and rural settlements.

Модернізація розкидача органічних добрив «ПРТ-10» для використання в технології механізованого компостування

The purpose of the work is to present the results of testing mock-up samples of technical devices and equipment for the «PRT-10» organic fertilizer spreader to ensure that they fulfill the functional capabilities of mechanized composting and meet the requirements of the technological regulations. Methods and materials. To form a shoulder width of 2.5-3.5 m, a modernized spreader of organic fertilizers of the «PRT-10» type with replaceable drum-milling working bodies was used. Mock-up samples of the working bodies proposed by the author were installed at the places of installation of the existing drums, the main structural difference of which is the presence of right and left spiral lines. The blade installations are directed toward each other, which ensures the movement of raw materials from the side walls to the middle of the container. At the same time, the design of the drive of the working bodies did not change. Results. One of the options for increasing the efficiency of compost production is the expansion of technological capabilities and the development of additional technical devices and equipment for the spreader of organic fertilizers «PRT-10». The design of the mechanized composting device proposed by the author is a separate replaceable module installed on the rear board at the location of two drums of the «PRT-10» serial device. The main purpose of the replaceable module is pre-grinding, mixing of components, and formation of the edge during the preparation of a multi-component mixture that accumulates in the spreader trailer in the technology of mechanized composting. The use in the construction of the «PRT-10» serial spreader of interchangeable drums with the right and left directions of blade installation provides the technological height of the formed edge up to 1.6-1.7 m. The width of the base of the edge is 2.5-3.0 m, which agrees with the basic width values captured by aerators-mixers. The productivity of the unloading tool is up to 100 t/h. A special device for moistening mixtures with a moisture content of 30-45% ensures the introduction of water up to 40-60 l/t. Calculations carried out by the author on the use of the modernized spreader of organic fertilizers «PRT-10» and the aerator-mixer «AZK-2» in the production of composts proved economic advantages in the form of a reduction in fuel consumption during 4 cycles of aeration of the mixture – by 2.5 times. Conclusions. The use of a modernized device on transport units makes it possible to reduce the number of technical means involved in auxiliary operations of mechanized composting. Compost production using the modernized «PRT-10» spreader is economically feasible in existing economic conditions up to 2.0-2.2 thousand tons per processing season. For larger volumes, it is more appropriate to use the «AZK-2» trailed aerator mixer. Key words: compost mixture, burt, modernized spreader, replaceable drum, attached device, moistening, straw layer, mixing, grinding.

Advancements of sequencing batch biofilm reactor for slaughterhouse wastewater assisted with response surface methodology

Slaughterhouse wastewater (SWW) contains a significant volume of highly polluted organic wastes. These include blood, fat, soluble proteins, colloidal particles, suspended materials, meat particles, and intestinal undigested food that consists of higher concentrations of organics such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen and phosphorus hence an efficient treatment is required before discharging into the water bodies. The effluent concentrations and performance of simultaneous sequential batch biofilm reactor (SBBR) with recycled plastic carrier media support are better than the local single-stage sequential batch reactor (SBR), which is lacking in the literature in terms of COD, NH3, NO3, and PO4 treatment efficiency. The present study reports a novel strategy to remove the above mentioned contaminants using an intermittently aerated SBBR with recycled plastic carrier media support along with simultaneous nitrification and denitrification. The central composite design was evaluated to optimize the treatment performance of seven different process variables including; different alternating conditions (Oxic/anoxic) for aeration cycles (3/2 h in a 6 h cycle, 6/5 h in a 12 h cycle and 9/8 h in an 18 h cycle) and hydraulic retention time (6, 12 and 18 h). The average removal efficiencies are 94.5% for NH3, 93% for NO3 and 90.1% for PO4, and 99% for COD. The study reveals that the denitrification in the post-anoxic phase was more efficient than the pre-anoxic phase for pollutant removal and maintaining higher quality effluent. The effluent concentrations and performance of simultaneous SBBR with recycled polyethylene carrier support media were better than local SBR system in terms of COD, NH3, NO3 and PO4 treatment efficiency. Results stipulated the suitability of SBBR for wastewater treatment and reusability as a sustainable approach for wastewater management under optimum conditions.

Optimizing aeration pattern to improve nitrogen treatment performance of ditch wetlands in polder areas around Chaohu Lake, China

Ditch wetlands in polders are planned to attenuate the nitrogen load from paddy fields, mainly resulting in eutrophication of Chaohu Lake, China. The nitrogen treatment performance of ditch wetlands is poor because of the low dissolved oxygen (DO) concentration observed in field. Aeration is often used to improve both DO concentration and nitrogen treatment performance, but aeration pattern needs to be optimized for better treatment performance. A dynamic model was constructed to explore the nitrogen transformation with the DO effect. The simulation results show that through an optimal aeration pattern, the treatment performance of total nitrogen (TN) increased from 3.9% to 23.9% when TN was dominated by ammonium and organic nitrogen (NH4 + ON). The optimal aeration pattern was that the ratio of aeration time to non-aeration time was approximately 1:1, and the aeration cycle period was equal to the experimental period (10 d). The essence of aeration is to ensure that the mass of nitrogen nitrified from NH4 is denitrified, which means that the rate of nitrification is close to that of denitrification. The concentration ratio of (NH4 + ON)/NO3 was a reasonable indicator to determine the aeration time for various composition of TN. Finally, guidelines for drainage water recycling within polders from the point of DO are provided to achieve the objective of nitrogen load reduction in polders.

Achieving Partial Nitritation in Anammox Start-Up Environment

Removing ammonium via the partial nitritation anammox (PNA) process has been widely applied because of its cost and energy effectiveness. However, the first stage of PNA, partial nitritation, is hard to implement practically due to the challenging suppression of nitrate oxidizing bacteria (NOB) and should be achieved in the anammox environment to extend it to one stage PNA. Hence, this article evaluates different techniques, such as the combination of low dissolve oxygen (DO) and high free ammonia (FA), and the intermittent aeration cycle to achieve partial nitritation in an anammox start-up environment. For this purpose, a 10.5 L lab-scale moving bed biofilm reactor was set up and fed with synthetic wastewater and the transformation of influent ammonium into nitrate and nitrite was measured. The results showed that, despite applying low DO and higher free ammonia than the inhibition range of NOB, the nitrate production rate (NPR) was consistently higher than the nitrite accumulation rate (NAR), signifying no sufficient NOB suppression, partial nitritation under continuous aeration and up to a 0.27 gN/m2·d surface ammonium loading rate (SALR). Higher SALR than 0.27 gN/m2·d could result in partial nitritation since nitrogen compounds transformation was closer to partial nitritation when the reactor was subjected to 0.27 gN/m2·d rather than 0.14 gN/m2·d. Lifting up the SALR, on the other hand, results in a bad anammox environment and cannot prolong it to one-stage PNA. An intermittent aeration cycle with four different cycle lengths sets, obtained by monitoring nitrogen compound transformation, was, therefore, applied to the reactor. The relatively shorter aerobic length of 10 min ON and 30 OFF intermittent aeration cycle with 0.5 mg/L aerated DO was successful in achieving the partial nitritation with NPR, NAR, and ammonium removal efficiency (ARE) values of 17%, 78%, and 37%, respectively, showing that shorter aerated length suppresses NOB to a high degree due to less available time for NOB after oxygen starvation.

Energy savings with a biochemical oxygen demand (BOD)- and pH-based intermittent aeration control system using a BOD biosensor for swine wastewater treatment

Intermittently aerated activated sludge processes save energy by minimizing the total aeration time per day without deteriorating effluent water quality. Swine wastewater contains high, often widely fluctuating concentrations of biochemical oxygen demand (BOD) and nitrogen. BOD-based aeration control would therefore be a useful method to reduce the energy demands of aeration, but requires a reliable BOD sensor for swine wastewater. In this study we developed a novel approach for BOD- and pH-based intermittent aeration control (BAC) using a BOD biosensor based on exoelectrogenic bacteria and tested it at four swine wastewater treatment plants. This BAC system reduced aeration energy in the plants by 15–36% compared to fixed aeration cycle operations while maintaining low concentrations of BOD and total nitrogen in the effluent. The energy saved per wastewater volume was 477–1012 kWh/m3/yr, equivalent to a reduction of 2.2–7.0 t-CO2/m3/yr in greenhouse gas emissions. The biosensor was equipped with an internet connection to allow for remote monitoring of water quality data with a smartphone, saving labour in the operational management of the plants. Aquabacterium and the aerobic denitrifier Thauera were detected as the predominant genera in the activated sludge.

Energy Flexibility Chances for the Wastewater Treatment Plant of the Benchmark Simulation Model 1

Future energy systems must mainly generate electricity from renewable resources. To deal with the fluctuating availability of wind and solar power, new versatile electricity markets and sustainable solutions concentrating on energy flexibility are needed. In this research, we investigated the potential of energy flexibility achieved through demand-side response for the wastewater treatment plant of the Benchmark Simulation Model 1. First, seven control strategies were simulated and assessed. Next, the flexibility calls were identified, two energy flexibility scenarios were defined and incorporated into the model, and the control strategies were evaluated anew. In this research, the effluent ammonia concentration needed to be maintained within the limits for as long as possible. Strategy 5, which controlled ammonia in Tank 5 at a low value and did not control any nitrate in Tank 2, of Scenario 1, which was characterized by an undetermined on/off aeration cycle, was then found to be the best. Although this control strategy led to high total energy consumption, the percentage of time during which aeration was nearly suspended was one of the highest. This work proposes a methodology that will be useful to plant operators who should soon reduce energy consumption during spikes in electricity prices.

Exploring the Meta-regulon of the CRP/FNR Family of Global Transcriptional Regulators in a Partial-Nitritation Anammox Microbiome.

ABSTRACTMicroorganisms must respond to environmental changes to survive, often by controlling transcription initiation. Intermittent aeration during wastewater treatment presents a cyclically changing environment to which microorganisms must react. We used an intermittently aerated bioreactor performing partial nitritation and anammox (PNA) to investigate how the microbiome responds to recurring change. Meta-transcriptomic analysis revealed a dramatic disconnect between the relative DNA abundance and gene expression within the metagenome-assembled genomes (MAGs) of community members, suggesting the importance of transcriptional regulation in this microbiome. To explore how community members responded to cyclic aeration via transcriptional regulation, we searched for homologs of the catabolite repressor protein/fumarate and nitrate reductase regulatory protein (CRP/FNR) family of transcription factors (TFs) within the MAGs. Using phylogenetic analyses, evaluation of sequence conservation in important amino acid residues, and prediction of genes regulated by TFs in the MAGs, we identified homologs of the oxygen-sensing FNR in Nitrosomonas and Rhodocyclaceae, nitrogen-sensing dissimilative nitrate respiration regulator that responds to nitrogen species (DNR) in Rhodocyclaceae, and nitrogen-sensing nitrite and nitric oxide reductase regulator that responds to nitrogen species (NnrR) in Nitrospira MAGs. Our data also predict that CRP/FNR homologs in Ignavibacteria, Flavobacteriales, and Saprospiraceae MAGs sense carbon availability. In addition, a CRP/FNR homolog in a Brocadia MAG was most closely related to CRP TFs known to sense carbon sources in well-studied organisms. However, we predict that in autotrophic Brocadia, this TF most likely regulates a diverse set of functions, including a response to stress during the cyclic aerobic/anoxic conditions. Overall, this analysis allowed us to define a meta-regulon of the PNA microbiome that explains functions and interactions of the most active community members.IMPORTANCE Microbiomes are important contributors to many ecosystems, including ones where nutrient cycling is stimulated by aeration control. Optimizing cyclic aeration helps reduce energy needs and maximize microbiome performance during wastewater treatment; however, little is known about how most microbial community members respond to these alternating conditions. We defined the meta-regulon of a PNA microbiome by combining existing knowledge of how the CRP/FNR family of bacterial TFs respond to stimuli, with metatranscriptomic analyses to characterize gene expression changes during aeration cycles. Our results indicated that, for some members of the community, prior knowledge is sufficient for high-confidence assignments of TF function, whereas other community members have CRP/FNR TFs for which inferences of function are limited by lack of prior knowledge. This study provides a framework to begin elucidating meta-regulons in microbiomes, where pure cultures are not available for traditional transcriptional regulation studies. Defining the meta-regulon can help in optimizing microbiome performance.

The influence of aeration control and temperature reduction on nitrogen removal and microbial community in two anammox‐based hybrid sequencing batch biofilm reactors

AbstractBACKGROUNDTwo hybrid biofilm reactors, an integrated fixed‐film activated sludge–sequencing batch reactor (IFAS‐SBR) and a hybrid SBR with a mixture of activated sludge and granules, were used to reach enhanced nitrogen removal based on the anaerobic ammonium oxidation (anammox) process under intermittent aeration.RESULTSIFAS‐SBR reached a more stable performance after a rapid start‐up period of 25 days, and it showed a more reliable performance than the other reactor. The highest nitrogen removal efficiency (NRE) was up to 99% based on NH4+‐N concentration and 91% based on total nitrogen concentration (TIN). A nitrogen removal rate of 0.01 to 0.15 kgN m−3 d−1 was achieved throughout the operation based on the TIN. The set‐point of maximum dissolved oxygen (DO) at the peak of each aeration cycle was maintained at 1.2 ± 0.1 mg L−1. The optimum working range for daily average DO concentration was 0.2–0.7 mg L−1. Cold temperatures caused a decline of NRE, but NRE &gt; 50% for temperatures above 13 °C was achieved.CONCLUSIONSResults implied a higher abundance of Candidatus brocadia species of anammox bacteria in the biofilm samples and Denitratisoma genus in the flocs. The most substantial contribution of shared taxa among all samples at class level was Betaproteobacteria and Gammaproteobacteria, and the least abundant class was Nitrospira. Overall, results implied that IFAS‐SBR is a robust configuration for anammox‐based nitrogen removal in sidestream, and controlled intermittent aeration could suppress nitrite oxidation and help to regain system efficiency.

Influence of substrates concentrations on the dynamics of oxygen demand and aeration performance in ideal bioreactors

The effect of bioreactor configurations on the dynamics of aeration modelling was investigated by incorporating three different correlations from the literature to estimate α-factors into the aeration model. Estimated air flow rates using the three correlations were then validated against experimental data obtained from pilot sequencing batch reactors (SBRs). Two identical SBRs were operated in parallel; one received raw wastewater and the other received primary treated wastewater. The validated aeration model was then used to evaluate aeration dynamics in different bioreactor configurations, both for nitrification only and nitrification/denitrification, with the three different correlations. The current study is the first to investigate the validity of the aforementioned correlations using various bioreactor configurations and to establish that the bioreactor configuration not only impacts spatial and temporal biological oxygen demands as currently understood but also oxygen transfer efficiency. The first correlation based on the real-time bioreactor soluble chemical oxygen demand (sCOD) was able to predict the temporal measured air flow rate in the pilot SBRs. The second correlation based on the influent COD overestimated the air flow rates as it considered the impact of the influent loading rates on the α-factor and overlooked the improvement in α-factor due to biodegradation. The third correlation based on MLSS concentrations underestimated the air flow rates at the beginning of the aeration cycle as it ignored the impact of influent loading rates on the α-factor and considered only the insignificant change in MLSS during the aeration cycle. In terms of bioreactor configuration, the model-based analysis showed that the first correlation is suitable for designing SBR, plug flow reactor (PFR), step-feed PFR, and completely mixed stirred reactor (CSTR) systems, and the third correlation is suitable for designing CSTRs and membrane bioreactors (MBRs), while the second correlation was not accurate in any of the reactors modelled. When nitrification was targeted, the CSTR reduced aeration energy by 44 %–49 % compared to the PFR, and 41 %–43 % when both nitrification and denitrification were targeted. Compared to the plug-flow reactor, the step-feed PFR reduced aeration energy by 9% when nitrification only was targeted. However, when pre-denitrification was added, both systems showed the same aeration energy consumption. Pre-denitrification reduced organic loadings to aeration tanks and decreased aeration energy by 22 %, 11 %, 15 %, and 14 % in PFR, CSTR, PFR step feed and MBR systems, respectively.

RESEARCH ON IMPROVEMENT OF THE METHOD OF PERIODIC AERATION OF WASTEWATER

The aeration process is a key part of biological wastewater treatment technology. But, paradoxically, during the existence of this technology, it has not changed significantly. The process of aeration of wastewater remains the largest consumer of electricity in the entire complex of treatment facilities. The possibility of adjusting the duration of the aeration cycle depending on the "explosive" change in the amount of contaminants was stated. In this case, the system must respond to this "perturbation" and adjust the duration of the aeration cycle to provide the necessary oxygen regime of biological oxidation of contaminants. The research data on the method of periodic aeration based on a comparison of the concentration of oxygen in the liquid to be cleaned and in the gases leaving after aeration are presented. The basic principle is that the aeration system continues to supply oxygen, which is no longer able to diffuse into the aerated liquid, and comes to the surface, bypassing the process of mass transfer. The experimentally established method of adjusting the duration of aeration periods for implementation in one aeration tank can be applied to a whole group of aeration tanks. Using the method in the optimal mode for each of the specified number of aeration tanks is impossible without the use of a microprocessor. Therefore, a control method was developed that allows the application of a fundamentally new algorithm for periodic aeration. This algorithm allows to increase the growth of activated sludge and to increase the efficiency of wastewater treatment. To assess the possibility of stabilizing the operation of certain aeration tanks, in the implementation of intermittent aeration by the concentration of oxygen in the liquid, a model example was considered, from which follows the differential equation of oxygen balance in the liquid. The study of this equation for stability and behavior in the phase plane makes it possible to choose the conditions under which the periodic aeration algorithm will be the most efficient in terms of purification and energy consumption. Theoretical calculation gave a mathematical justification for the experimental data. Based on numerical calculations, the condition of optimal operation of the aeration system for a group of aeration tanks is derived. Thus, it was found that the optimal concentration of oxygen in the liquid at which to start aeration is 0.06-0.12 mg / dm3. Periodic aeration with a period of 30 minutes makes it possible to maintain a stable gradient of oxygen concentrations in the liquid. The productivity of treatment plants according to the developed algorithm of controlled aeration, in accordance with the concentration of oxygen in the liquid to be cleaned, ensures the rational use of electricity.

Organic Substances Reduction in Palm Oil Mill Effluent (POME) After Cultivation with Locally Isolated Microalgae

This work aims to study the ability of locally isolated microalgae to reduce organic substances in Palm Oil Mill Effluent (POME) which was carried out on a laboratory scale. Inoculum with a concentration of 20% was cultivated into POME media with various concentration of LP100 (without dilution), LP75 (25% dilution), and LP50 (50% dilution) using aeration and continuous lighting for 15 days in vessels with a lighting intensity of 1300 lux. Biomass of microalgae were observed daily and analyzed in dry weight by means of spectrophotometry using 624 nm wavelength to get their growth by determining the content of algae biomass. The reduction of organic substances in POME was observed by measuring the COD, BOD phosphate, ammonium, nitrate, and fatty oil parameters every 3 hours with the standard method. Results show that the growth of microalgae occurred well in POME media at LP75 and LP50 concentrations with inoculum concentration of 20% under 1300 lux lighting intensity conditions with a continuous 24-hour lighting and aeration cycle that obtained biomass content of 0.92 and 1.08 g-DW/L, respectively. The presence of microalgae in POME at concentration of LP75 for 12 days reduced organic substances and nutrients reaching 80.74% - 99.70%. Some parameters that were reduced include BOD (99.35%), COD (89.57%), TSS (89.68%), Phosphate (97.70%), Ammonium (95.08%), Fatty Oil (99.70%), and Nitrates (80.74%). This study concludes that locally isolated microalgae have ability to treat POME safely for environment and as a growing medium for microalgae followed by a decrease in organic substances.

Optimization of airflow and aeration cycles in a new structured bed reactor configuration for carbon and nitrogen removal

ABSTRACT The Structured Bed Reactor with Recirculation and Intermittent Aeration (SBRRIA) is a reactor configuration that presents high efficiency of organic matter and nitrogen removal, besides low sludge production. However, operational parameters, as the recirculation rate, aeration time, and airflow, are not fully established. A bench-scale structured bed reactor with intermittent aeration was fed with synthetic effluent simulating the characteristics of sanitary sewage. The reactor was operated for 280 days with an operational hydraulic retention time (HRT) of 10 h. The reactor was operated without effluent recirculation for the first time since this approach was not yet reported, and was named Structured Bed Reactor with Intermittent Aeration (SBRIA). The COD removal was higher than 81% for all operational conditions, and the total nitrogen removal ranged from 10 to 80%. The highest efficiencies were obtained with an aeration time of 1 h 45 min (total cycle of 3 h) and an airflow rate of 4.5 L.min−1. Different nitrification and denitrification behaviours were observed, resulting in nitrification efficiencies over 90% when the reactor was submitted to higher aeration times and denitrification efficiencies above 90% when the reactor was submitted to low aeration times. The airflow ranges tested in this study affected the nitrification and the total nitrogen efficiencies. Even without effluent recirculation, the temporal profile showed that there were no peaks in the concentration of the nitrogen forms in the reactor effluent, saving electrical energy up to 75% due to pumping.

Aeration and non-aeration cycles (AE/NA) time: influence in combined organic matter and nitrogen removal and features of biofilm

ABSTRACT This research aimed the performance evaluation of a structured bed reactor with different cycles of Intermittent Aeration (IA)(SBRRIA) in the municipal sewage treatment and the verification of the effect of IA cycles on the total nitrogen (TN) removal and organic matter (COD). Three IA cycles were evaluated: phase I (4 h AE (aeration on) – 2 h NA (aeration off)); II (2 h AE–1 h NA) and III (2 h AE–2 h NA), with Hydraulic Retention Time of 16 h. The best nitrogen removal was obtained during phase II, with the lowest non-aeration time: efficiency of nitrification, denitrification, TN and COD removal of 80 ± 15%, 82 ± 12%, 67 ± 6% and 94 ± 7%, respectively. The mean cell residence time was 19, 26 and 33 d in phases I, II and III, respectively. The statistical analysis applied to the AE/NA profiles showed that the time of AE and NA in the cycles did not influence nitrogen and organic matter removal. Thus, this indicates the recirculation and the gradient formed in the support material facilitate the process of Simultaneous Nitrification and Denitrification. The lowest concentration of nitrifying and denitrifying microorganisms was obtained in effluent and sludge at the end of phase III. From the TP (Total Proteins)/TPS (Total Polysaccharides) ratio obtained (0.8 ± 0.1, 1.3 ± 0.1 e 1.5 ± 0.1 in phases I, II and III), it was possible to conclude that the biofilm in phase I was more porous, with a thin layer if compared to that in phase II and III.

Simulation of Wastewater Depolution Processes by Advanced Biological Methods

This paper presents the results from a study which simulates wastewater depollution processes using advanced biological methods. The experimental research was performed in a static biological reactor, equipped with an air compressor and an agitator / mixer. Synthetic wastewater, prepared with the addition of glucose, was fed into the reactor. The wastewater was subjected to alternating cycles of aeration and slow mixing, for consecutive 3 h intervals within the reactor to ensure the necessary conditions for the reduction of nitrogen based organic compounds within the wastewater. In the successive aeration processes, aerobic / nitrifying microorganisms which developed within the reactor, facilitated the decomposition of organic substances into nitrites and then into nitrates. By stopping aeration and starting the slow mixing cycle the anaerobic / denitrifying microorganisms growing in the reactor consume the necessary oxygen from nitrates and release free nitrogen into the atmosphere, thus completing the process of advanced depollution. Therefore, the experimental procedure highlights the existence of two distinct phases in the development of the depollution process. In the first phase, the biological process is initiated using glucose in order to promote the growth of the bacterial flora. In the second phase (the regime phase), the reduction of mineral and organic pollutants from the wastewater is ensured. The activity of microorganisms in the biological reactor can be further supported by the recirculation of activated sludge retained in the secondary decanter. The proposed technology offers a fast, safe and relatively inexpensive method for advanced wastewater depollution. Bioreactors of this type are recommended in wastewater treatment schemes in the hearth of rural localities, agro-zootechnical complexes and tourist units with seasonal activities due to their fluctuations in hourly wastewater flow rates. Similar approaches can also be considered for the elimination of ammonium compounds in groundwater polluted with animal manure.

Evaluation of aerobic biological process with post-ozonation for treatment of mixed industrial and domestic wastewater for potential reuse in agriculture

Suspended growth biological process (SGBP) with post-ozonation (O3) was investigated for treatment of simulated complex mixed industrial and domestic wastewater at specific conditions. The SGBP was operated under complete aeration, 30/30-min and 60/30-min on/off aeration cycles and effluent was exposed to ozone at 250 mgO3/h fixed dose and contact time 1 to 60-min. The SGBP performance was maximum under 60/30-min aeration conditions achieving 92.1, 90.6, 83.3 and 83.8% reduction in COD, BOD5, TN and PO4-P respectively. Nitrification (64.1%) was uninhibited even on transition to pulse aeration cycles. The concentrations of diesel oil and methylene blue dye were reduced by 83.6 and 93.5% respectively. Post-ozonation oxidized residual organics up to 19.9%, based on COD measurement, and increased effluent BOD5 up to 49.5%. The results including the crop growth outcomes indicate that SGBP-O3 process has great potential to improve the quality of mixed industrial and domestic wastewater considerably for various water reuse applications.