Aeration Costs Research Articles

Removal of steroid estrogens from municipal wastewater in a pilot scale expanded granular sludge blanket reactor and anaerobic membrane bioreactor

Anaerobic treatment of municipal wastewater offers the prospect of a new paradigm by reducing aeration costs and minimizing sludge production. It has been successfully applied in warm climates, but does not always achieve the desired outcomes in temperate climates at the biochemical oxygen demand (BOD) values of municipal crude wastewater. Recently the concept of ‘fortification' has been proposed to increase organic strength and has been demonstrated at the laboratory and pilot scale treating municipal wastewater at temperatures of 10–17°C. The process treats a proportion of the flow anaerobically by combining it with primary sludge from the residual flow and then polishing it to a high effluent standard aerobically. Energy consumption is reduced as is sludge production. However, no new treatment process is viable if it only addresses the problems of traditional pollutants (suspended solids – SS, BOD, nitrogen – N and phosphorus – P); it must also treat hazardous substances. This study compared three potential municipal anaerobic treatment regimes, crude wastewater in an expanded granular sludge blanket (EGSB) reactor, fortified crude wastewater in an EGSB and crude wastewater in an anaerobic membrane bioreactor. The benefits of fortification were demonstrated for the removal of SS, BOD, N and P. These three systems were further challenged with the removal of steroid estrogens at environmental concentrations from natural indigenous sources. All three systems removed these compounds to a significant degree, confirming that estrogen removal is not restricted to highly aerobic autotrophs, or aerobic heterotrophs, but is also a faculty of anaerobic bacteria.

Current status of the rotating belt filtration (RBF) technology for municipal wastewater treatment

Rotating belt filtration (RBF) is a technology designed for the removal of suspended solids, and effluent organic matter from wastewater that has been recently undergoing intensive development and testing. Generally, RBF can remove solids to meet Ten State Standards (‘Primary settling of normal domestic wastewater can be expected to remove approximately one-third of the influent BOD5 when operating at an overflow rate of 41 m3/(m2 d) [1,000 gallons per day/square foot]’) and European council directive standards (at least 50% total suspended solids (TSS) and 20% Biological Oxygen Demand (BOD) removal). Recent testing have also shown that, when a polymer is added upstream of the RBF, solids and organics removal is significantly enhanced. Advantages of RBF include reduced space requirement, ability to support small mesh without clogging, reduced civil engineering site work, and modular construction allowing for reduced design work, faster installation, and ease of plant expansion. Additional site-specific advantages may include reduced capital and operation costs, and energy savings (e.g. reduced aeration costs following the addition of primary solids removal by RBF against the baseline case where primary solids removal is not practiced). As a matter of fact, when RBF is operated as a pretreatment to remove 50% of the incoming TSS prior to the biological aerated tank, a significant decrease in power consumption ranging from 22 to 28% can be expected if compared to the case where no primary treatment is used. This paper focuses on the current status of development of the technology and provides a literature review of recent experimental studies focused on testing RBF.

Synergistic carbon metabolism in a fast growing mixotrophic freshwater microalgal species Micractinium inermum

In recent years microalgae have attracted significant interest as a potential source of sustainable biofuel. Mixotrophic microalgae are able to simultaneously photosynthesise while assimilating and metabolising organic carbon. By combining autotrophic and heterotrophic metabolic pathways biomass productivity can be significantly increased. In this study, acetate-fed mixotrophic Micractinium inermum cultures were found to have a specific growth rate 1.74 times the sum of autotrophic and heterotrophic growth. It was hypothesised that gas exchange between the two metabolic pathways within mixotrophic cultures may have prevented growth limitation and enhanced growth. To determine the extent of synergistic gas exchange and its influence on metabolic activity, dissolved inorganic carbon (DIC), dissolved oxygen (DO) and photosynthesis and respiration rates were measured under different trophic conditions. A 32.7 fold and 2.4 fold increase in DIC and DO concentrations, relative to autotrophic and heterotrophic cultures respectively, were coupled with significant increases in rates of photosynthesis and respiration. These data strongly support the hypothesis of mixotrophic gas exchange within M. inermum cultures. In addition to enhanced growth, this phenomenon may provide reductions in aeration and oxygen stripping costs related to microalgae production.

Modelling simultaneous anaerobic methane and ammonium removal in a granular sludge reactor

Anaerobic nitrogen removal technologies offer advantages in terms of energy and cost savings over conventional nitrification–denitrification systems. A mathematical model was constructed to evaluate the influence of process operation on the coexistence of nitrite dependent anaerobic methane oxidizing bacteria (n-damo) and anaerobic ammonium oxidizing bacteria (anammox) in a single granule. The nitrite and methane affinity constants of n-damo bacteria were measured experimentally. The biomass yield of n-damo bacteria was derived from experimental data and a thermodynamic state analysis. Through simulations, it was found that the possible survival of n-damo besides anammox bacteria was sensitive to the nitrite/ammonium influent ratio. If ammonium was supplied in excess, n-damo bacteria were outcompeted. At low biomass concentration, n-damo bacteria lost the competition against anammox bacteria. When the biomass loading closely matched the biomass concentration needed for full nutrient removal, strong substrate competition occurred resulting in oscillating removal rates. The simulation results further reveal that smaller granules enabled higher simultaneous ammonium and methane removal efficiencies. The implementation of simultaneous anaerobic methane and ammonium removal will decrease greenhouse gas emissions, but an economic analysis showed that adding anaerobic methane removal to a partial nitritation/anammox process may increase the aeration costs with over 20%. Finally, some considerations were given regarding the practical implementation of the process.

Effect of Different Mulches on Soil Moisture, Growth and Yield of Eureka Lemon (Citrus limonBurm) Under Rainfed Condition

An experiment was conducted during 2009–2011 to assess the effect of different mulches (bajra straw, maize straw, grasses, brankad (Adhotada vassica), farmyard manure and black polyethylene) on soil moisture, weed reduction, growth and yield in Eureka lemon (Citrus limon Burm). Different organic and inorganic mulches significantly increased the soil moisture status in various soil depths. Black polyethylene mulch recorded the maximum moisture content followed by farmyard manure and brankad. The black polyethylene and farmyard manure were found to be more effective in producing maximum growth extension than rest of the treatments although the differences were non-significant among the treatments. Plots treated with black polyethylene mulch recorded highest yield (1848 kg/ha) followed by farmyard manure (1780 kg/ha) and brankad (1744 kg/ha). Poor aeration, non-decomposable nature and high cost are the constraints of using black polyethylene as mulch material. Among the organic mulches, the cost of brankad was less as the material is easily available in local areas followed by bajra straw, maize straw and grasses.

Scenedesmus dimorphus와 질산화 박테리아의 공배양이 하수고도처리능에 미치는 영향

This study investigated the effect of a co-culture of Scenedesmus dimorphus and nitrifiers using artificial wastewater on the removal of ammonium, nitrate and phosphate in the advanced treatment. To test the synergistic effect of the co-culture, we compared the co-culture treatment with the cultures using S. dimorphus-only and nitrifiers-only treatment as controls. After 6 days of incubation, nitrate was removed only in the co-culture treatment and total amount of N removal was 1.3 times and 1.6 times higher in the co-culture treatment compared to those in the S. dimorphus- and nitrifiers-only treatments, respectively. In case of total amount of P, co-culture treatment removed 1.2 times and 12 times more P than the S. dimorphus -and nitrifiers-only conditions, respectively. This indicates that the co-culture improved removal rates for ammonium, nitrate, and phosphate. This further implies that there was no need for denitrification of nitrate and luxury uptake of P processes because nitrate and phosphate can be removed from the uptake by S. dimorphus. In addition, co-culture condition maintained high DO above 7 mg/L without artificial aeration, which is enough for nitrification, implying that co-culture has a potential to decrease or remove aeration cost in the wastewater treatment plants.

Effect of sensor location on controller performance in a wastewater treatment plant.

Complete mixing is hard to achieve in large bioreactors in wastewater treatment plants. This often leads to a non-uniform distribution of components such as dissolved oxygen and, hence, the process rates depend on them. Furthermore, when these components are used as input for a controller, the location of the sensor can potentially affect the control action. In this contribution, the effect of sensor location and the choice of setpoint on the controller performance were examined for a non-homogeneously mixed pilot bioreactor described by a compartmental model. The impacts on effluent quality and aeration cost were evaluated. It was shown that a dissolved oxygen controller with a fixed setpoint performs differently as a function of the location of the sensor. When placed in a poorly mixed location, the controller increases the aeration intensity to its maximum capacity leading to higher aeration costs. When placed just above the aerated zone, the controller decreases the aeration rate resulting in lower dissolved oxygen concentrations in the remainder of the system, compromising effluent quality. In addition to the location of the sensor, the selection of an appropriate setpoint also impacts controller behavior. This suggests that mixing behavior of bioreactors should be better quantified for proper sensor location and controller design.

Model predictive control of biological nitrogen removal via partial nitrification at low carbon/nitrogen (C/N) ratio

The shortage of easily degradable carbon source in the denitrification process limits the biological nitrogen removal efficiency. Partial nitrification has shown to be an attractive technology due its savings in aeration and external carbon source addition cost in the biological nitrogen removal. In this article, a model predictive control method was proposed to optimize the aeration and the external carbon source addition under the disturbance of influent flow rate and nitrogen load. The results indicated that 56% saving in external carbon source addition and 26% saving in aeration cost can be achieved by the model predictive control method applied in the partial nitrification, in comparison to the complete nitrification.

암모니아 센서를 이용한 간헐폭기 Membrane bioreactor공정에서의 전력비 저감과 관형막을 이용한 슬러지 농축에 관한 연구

It is essential to decrease energy consumption and excess sludge to economically operate sewage treatment plant. This becomes more important along with a ban on sea dumping and exhaustion of resource. Therefore, many researchers have been study on energy consumption reduction and strategies for minimization of excess sludge production from the activated sludge process. The aeration cost account for a high proportion of maintenance cost because sufficient air is necessary to keep nitrifying bacteria activity of which the oxygen affinity is inferior to that of heterotrophic bacteria. Also, additional costs are incurred to stabilize excess sludge and decrease the volume of sludge. There were anoxic, aerobic, membrane, deairation and concentration zone in this MBR process. Continuous aeration was provided to prevent membrane fouling in membrane zone and intermittent aeration was provided in aerobic zone through ammonia sensor. So, there was the minimum oxygen to remove below limited quantity that could be eliminated in membrane zone. As the result of this control, energy consumption of aeration system declined by between 10.4 % and 19.1 %. Besides, we could maintain high MLSS concentration in concentration zone and this induced the microorganisms to be in starved condition. Consequentially, the amount of excess sludge decrease by about 15 %.

Intermittent aeration affects the bioremediation potential of two red algae cultured in finfish effluent

The high cost of aeration needed to tumble culture macroalgae is a limiting factor for integration with land-based finfish culture. Toward reducing this electricity cost, we compared intermittent aeration (16 h on:8 h off) with continuous aeration (24 h on) on the productivity of two strains of Chondrus crispus (Basin Head and Charlesville) and Palmaria palmata from Atlantic Canada between May and June 2011. Algal fronds were cultured under a 16:8-h light/dark photoperiod in 50-L tanks supplied with finfish effluent (49 μmol L−1 of ammonium and 11 μmol L−1 of phosphate) at a mean water flow rate of 0.4 L min−1. Nitrogen (N) influx was 1.8 gN m−2 day−1, and phosphorus (P) influx was 0.9 gP m−2 day−1, with uptake rates ranging from 0.02 to 2.4 gN m−2 day−1 and −0.2 to 0.4 gP m−2 day−1. On average, the macroalgae culture system (algae and biofilms) removed 1.0 gN m−2 day−1 (51.9 %). The growth of macroalgae (pooled across treatment and strain) ranged from 0.5 to 1.6 % day−1, which accounted for a yield of 2.2 to 5.4 g DW m−2 day−1. Switching off aeration at night improved the growth rate of Basin Head Chondrus by 146 % and had no effect on growth rate or nitrogen and carbon removal by P. palmata and Charlesville Chondrus. Growth and yield of Basin Head Chondrus under intermittent aeration were over two times greater than both Charlesville Chondrus treatments.

Aeration Control with Gain Scheduling in a Full-scale Wastewater Treatment Plant

Process control is important at wastewater treatment plants to meet effluent criteria and minimise resource use. In a nitrogen removal plant, the aeration costs in the biological treatment part constitute the largest single electricity user at the plant. This study has investigated gain scheduling PI control at the Käppala wastewater treatment plant in full-scale operation and by simulation using a calibrated model of the plant. The aim was to vary the controller settings based on the nitrogen removal performance to achieve an energy saving. The best results were reached when scheduling the controller output limit, achieving a higher energy saving compared to a controller without gain scheduling.

Ammonia‐Based Feedforward and Feedback Aeration Control in Activated Sludge Processes

Aeration control at wastewater treatment plants based on ammonia as the controlled variable is applied for one of two reasons: (1) to reduce aeration costs, or (2) to reduce peaks in effluent ammonia. Aeration limitation has proven to result in significant energy savings, may reduce external carbon addition, and can improve denitrification and biological phosphorus (bio-P) performance. Ammonia control for limiting aeration has been based mainly on feedback control to constrain complete nitrification by maintaining approximately one to two milligrams of nitrogen per liter of ammonia in the effluent. Increased attention has been given to feedforward ammonia control, where aeration control is based on monitoring influent ammonia load. Typically, the intent is to anticipate the impact of sudden load changes, and thereby reduce effluent ammonia peaks. This paper evaluates the fundamentals of ammonia control with a primary focus on feedforward control concepts. A case study discussion is presented that reviews different ammonia-based control approaches. In most instances, feedback control meets the objectives for both aeration limitation and containment of effluent ammonia peaks. Feedforward control, applied specifically for switching aeration on or off in swing zones, can be beneficial when the plant encounters particularly unusual influent disturbances.

Biodegradation of a surrogate naphthenic acid under denitrifying conditions

Extraction of bitumen from the shallow oil sands generates extremely large volumes of waters contaminated by naphthenic acid which pose severe environmental and ecological risks. Aerobic biodegradation of NA in properly designed bioreactors has been investigated in our earlier works. In the present work, anoxic biodegradation of trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA) coupled to denitrification was investigated as a potential ex situ approach for the treatment of oil sand process waters in bioreactors whereby excessive aeration cost could be eliminated, or as an in situ alternative for the treatment of these waters in anoxic stabilization ponds amended with nitrate. Using batch and continuous reactors (CSTR and biofilm), effects of NA concentration (100–750mgL−1), NA loading rate (up to 2607.9mgL−1h−1) and temperature (10–35°C) on biodegradation and denitrification processes were evaluated. In the batch system biodegradation of trans-4MCHCA coupled to denitrification occurred even at the highest concentration of 750mgL−1. Consistent with the patterns reported for aerobic biodegradation, increase in initial concentration of NA led to higher biodegradation and denitrification rates and the optimum temperature was determined as 23–24°C. In the CSTR, NA removal and nitrate reduction rates passed through a maximum due to increases in NA loading rate. NA loading rate of 157.8mgL−1h−1 at which maximum anoxic NA and nitrate removal rates (105.3mgL−1h−1 and 144.5mgL−1h−1, respectively) occurred was much higher than those reported for the aerobic alternative (NA loading and removal rates: 14.2 and 9.6mgL−1h−1, respectively). In the anoxic biofilm reactor removal rates of NA and nitrate were dependent on NA loading rate in a linear fashion for the entire range of applied loading rates. The highest loading and removal rates for NA were 2607.9 and 2028.1mgL−1h−1, respectively which were at least twofold higher than the values reported for the aerobic biofilm reactor. The highest nitrate removal rate coincided with maximum removal rate of NA and was 3164.7mgL−1h−1.

Positive effect of reduced aeration rate on secretion of alpha-amylase and neutral proteases during pressurised fermentation of thermophilic Bacillus caldolyticus

The thermophilic microorganism Bacillus caldolyticus was incubated in laboratory scale stirred bioreactors under pressurised conditions at different aeration rates. Increased amounts of CO2/bicarbonate were solubilised under the chosen conditions. A reduction in aeration rate from 1 vvm to 0.1 vvm resulted in accumulation of CO2 and bicarbonate up to 126 mg l(-1) and 733 mg l(-1), respectively and also increased secretion of α-amylase and neutral proteases (increases of 123% and 52%, respectively). In this paper, the effect of reduced aeration rate on CO2/bicarbonate concentration and enzyme activities is presented. The selected fermentation conditions are closely related to those prevalent in large scale bioreactors and may offer the possibility of achieving high enzyme yields at reduced aeration costs on an industrial scale.

Achieving partial nitrification in a novel six basins alternately operating activated sludge process treating domestic wastewater

A novel technology was developed to achieve partial nitrification at moderately low DO and short HRT, which would save the aeration cost and have the capacity to treat a wide range of low-strength real wastewater. The process enables a relatively stable whereas nitrite accumulation rate (NO2-AR) was stabilized over 94% in the last aerobic basin on average of each phase through a combination of short HRT and low DO level. Low DO did not produce sludge with poorer settleability. The morphology and internal structure of the granular sludge was observed by using a scanning electron microscope (SEM) analysis during a long-term operation. The images indicated that thick clusters of spherical cells and small rod-shaped cells (NOB and AOB are rod-shaped to spherical cells) were the dominant population structure, rather than filamentous and other bacteria under a combination of low DO and short HRT, which gives a good indication of nitrite accumulation achievement. MPN method was used to correlate AOB numbers with nutrient removal. It showed that an ammonia-oxidizing bacterium (AOB) was the dominant nitrifying bacteria, whereas high NO2-AR was achieved at AOB number of 5.33×108 cell/g MLSS. Higher pollutant removal efficiency of 86.2%, 98% and 96.1%, for TN, NH4+-N, and TP, respectively, was achieved by a novel six basin activated sludge process (SBASP) at low DO level and low C/N ratio which were approximately equal to the complete nitrification-denitrification with the addition of sodium acetate (NaAc) at normal DO level of (1.5–2.5 mg/L).

Selection of aerators for intensive aquacultural pond

Aeration cost is the third largest cost in intensive aquaculture system after post larvae and feed cost representing about 15% of total production cost. Therefore, selection of aerators plays a major role in maximizing the profit in such system. Over the years, various types of aerators have been developed specifically to enhance the production of aquatic species. The performances of these aerators are generally compared in terms of standard aeration efficiency. However, suitability of a particular aerator at different pond sizes and water quality conditions can best be determined in terms of aeration cost per unit time of operation. In the present study, economic performance of five different aeration systems – circular stepped cascade (CSC), pooled circular stepped cascade (PCSC), 1-hp paddle wheel, 2-hp paddle wheel and propeller aspirator pump were evaluated and compared at different pond sizes, initial DO concentrations of pond and operating hours of aerators; assuming a typical Indian major carp (IMC) culture with commonly practiced stocking density and feeding. Both CSC and PCSC aerators were found to be suitable for pond size less than 1000m3. However, for pond sizes more than 5000m3, 1-hp paddle wheel and 2-hp paddle wheel aerators were found to be efficient.

The regulation and control strategies of a sequencing batch reactor for simultaneous nitrification and denitrification at different temperatures

The performance of a sequencing batch reactor for simultaneous nitrification and denitrification (SBR–SND) was investigated under 5–30°C and strategies against temperature influences were proposed. Aeration of 8, 7, 7 and 6h were sufficient for 5±2, 10±2, 20±2 and 30±2°C, respectively. Further extension was insubstantial, only increased the aeration cost. The adjustment of C/N ratio to offset the temperature impacts was not remarkable. Prolonged sludge retention time lessened the influences of low temperature but deteriorated the system at high temperature. The oxidation reduction potential, the dissolved oxygen concentration, the sludge volume index and the extracellular polymeric substances amount changed with temperature alterations and thus affected the system performance. In conclusion, measures should be taken for temperature oscillations and the regulation and control of the operational parameters could alleviate the influences of temperature on the performances of the SBR–SND system.

Biological nutrient removal with limited organic matter using a novel anaerobic–anoxic/oxic multi-phased activated sludge process

An anaerobic–anoxic/oxic (A2/O) multi-phased biological process called “phased isolation tank step feed technology (PITSF)” was developed to force the oscillation of organic and nutrient concentrations in process reactors. PITSF can be operated safely with a limited carbon source in terms of low carbon requirements and aeration costs whereas NAR was achieved over 95% in the last aerobic zone through a combination of short HRT and low DO levels. PCR assay was used for XAB quantification to correlate XAB numbers with nutrient removal. PCR assays showed, high NAR was achieved at XAB population 5.2×108cells/g MLVSS in response to complete and partial nitrification process. It was exhibited that low DO with short HRT promoted XAB growth. Simultaneous nitrification and denitrification (SND) via nitrate were observed obviously, SND rate was between 69–72%, at a low DO level of 0.5mg/l in the first aerobic tank during main phases and the removal efficiency of TN, NH4+-N, COD, TP was 84.7 .97, 88.3 and 96% respectively. The removal efficiencies of TN, NH4+-N, and TP at low C/N ratio and DO level were 84.2, 98.5 and 96.9% respectively which were approximately equal to the complete nitrification–denitrification with the addition of external carbon sources at a normal DO level of (1.5–2.5mg/l).

ORP slope and feast–famine strategy as the basis of the control of a granular sequencing batch reactor treating winery wastewater

Winery wastewater is characterized by a high variability of its organic content, and flexible systems such as granular sequencing batch reactors (GSBRs) are required for its treatment. Despite the high load capacity inherent to these systems, the operation with a predetermined cycle length is not suitable to withstand high COD fluctuations. In this study, a control system able to automatically control the HRT depending on the actual organic load has been designed. The relation between ORP slope and DO profiles with the COD consumption together with a proper periodic starvation time are the basis of the control strategy. GSBR operation using the designed system led to an organic matter removal up to 95% for a wide range of organic matter concentrations (1–8g/L), optimizing cycle duration and avoiding unnecessary aeration costs. The reactor showed a high stability and a rapid response to sudden changes in the COD influent concentration. Biomass settleability remained almost constant around 95m/h and aggregates showed a Feret diameter of 4–6mm and sphericity up to 0.8.

Aeration Cost of Propeller-Aspirator Pump Aerator at Optimum Geometric and Dynamic Conditions

Aeration Cost of Propeller-Aspirator Pump Aerator at Optimum Geometric and Dynamic Conditions