Aerated Stabilization Basin Research Articles

Investigation of cyanobacteria blooms in paper mill wastewaters and assessment of zinc as a control agent

At a paper manufacturing mill (PML) that had been previously part of an integrated pulp (bisulphite) and paper mills industry, cyanobacterial blooms were observed in the mill’s aerated stabilization basin (ASB) ponds at about 3 years after pulping had been discontinued. This study aimed to determine the factors that led to bloom occurrences and potential control strategies applicable to the paper manufacturing mill’s, aerated stabilization basin system that discharges wastewaters into a coastal lake. Following discontinuation of pulping, the colour of the wastewaters reduced to low levels (~ 10 Hazen units or less), while the levels of nutrient remained potentially supportive of cyanobacteria growth with total phosphorus at ~ 0.1 mg/L and total nitrogen at > 2.5 mg/L. Incidences of blooms in the ABS were associated with preceding average monthly rainfalls and wind speeds being less (~ 44% and ~ 7%, respectively) and average direct sunlight hours being greater (~ 9%) than the long-term average values. Zinc was investigated for control of cyanobacteria as this metal is less toxic to aquatic organisms and microflora than copper algaecides. In laboratory culture trials, zinc was found to inhibit growth of M. aeruginosa (strain MIC338) and Pseudanabaena sp. when dosed at ~ 2.5 mg/L. The inhibition of cyanobacteria by zinc was found to vary between ASB pond samples which had different in situ chlorophyll a levels. This study found that the PML wastewaters investigated can be supportive of cyanobacterial growth to bloom levels after discontinuation of pulping processes and that zinc has potential as a cyanobacteria control agent.

Study of the impacts of process changes of a pulp and paper mill on aerated stabilization basin (ASB) performance

A laboratory scale (LS) and a field-based pilot plant (PP), designed to simulate aerobic stabilization basin (ASB) operation, were utilized to assess the potential impacts of changes in pulp and paper (P&P) mill operations on full-scale (FS) ASB performance. Two stages of investigation were conducted. The first was undertaken to determine the potential of pre-alum treatment of pulp mill wastewaters on ASB performance. The second investigation was conducted to assess ASB performance where wastewaters transitioned from being coagulated pulp and paper mill wastewaters to paper mill wastewaters only. Simulation ASB performance was assessed based on removals of BOD5, colour, UV@254 nm and nutrients [total phosphorus (TP) and nitrogen compounds (TN)]. Pre-alum treatment of pulp mill wastewaters with subsequent ASB treatment following mixing with paper mill wastewaters showed high percentage removals of BOD5. Despite low TP concentrations (≤0.05 mg/L) and low nutrient to BOD5 ratios of wastewaters in the LS-ASB trial, the high % BOD5 removal indicated recycling of nutrients from sludge [sourced from the FS-ASB]. Despite coagulation of pulp mill wastewater being performed using a very high alum dose (∼2000 mg/L) to remove colour and its precursors, colour formation remained high throughout the simulated ASB trials. Simulation of discontinuation of pulping indicated that colour would reduce rapidly to low levels in ASB wastewaters, but that TP and TN concentrations would persist for longer periods of time and decline slowly. Survey data of water qualities of the FS-ASB system obtained before, during and 2 years after discontinuation of pulping are presented.

An introduction to optimizing supplemental nutrients at pulp and paper wastewater treatment plants

Development and maintenance of mill- and wastewater treatment system-specific programs aimed at optimizing use of supplemental nutrients for purposes of minimizing residual nutrients in treated effluents have evolved in recent years and are summarized. Suggestions for monitoring of nutrient forms in wastewaters prior to and during biological treatment are presented, as are approaches for determining supplemental nutrient requirements, monitoring biomass characteristics, and achieving minimum nitrogen and phosphorus residuals in treated final effluents while maintaining targeted levels of biological treatment. Aspects of nutrient management relevant to activated sludge (AS) and aerated stabilization basin (ASB) systems are presented, and ASB configurations operated in part to minimize nutrient levels in treated effluents are highlighted.

Fate and biotransformation of phytosterols during treatment of pulp and paper wastewater in a simulated aerated stabilization basin

Pulp and paper wastewater (PPW) contains significant concentrations of phytosterols, suspected of inducing endocrine disruption in aquatic species. Aerated stabilization basins (ASBs) are commonly used for the treatment of PPW, but phytosterol removal varies among treatment systems. The objective of this study was to better understand the removal processes and biotransformation of phytosterols within an ASB treatment system fed with untreated PPW. PPW settled solids and supernatant fractions showed that phytosterols are primarily associated with settleable solids, which carry phytosterols to ASB sediment where anoxic/anaerobic conditions prevail. Bioassays with supernatant and settled PPW fractions of the raw wastewater conducted under aerobic and anaerobic conditions, respectively, showed that solids disintegration and hydrolysis results in phytosterol release in ASBs. A simulated ASB, fed with PPW and operated for 2.4 years at three hydraulic retention times (HRTs; 22.2, 11.1 and 5.6 d) with total phytosterol and solids loading rates from 10 to 42 μg/L-d and 44–178 mg/L-d, respectively, was used to determine the steady-state effluent quality and sediment characteristics. Although effluent COD and phytosterol concentrations were relatively low and stable (84–88% total COD removal; 82–94% total phytosterol removal) across the range of HRTs tested, sediment COD and phytosterol concentrations increased with increasing loading rate. On average, 51% of the phytosterols entering the ASB were removed via biotransformation, 40% were retained in the sediment, and the remaining 9% exited with the effluent. This study demonstrates the role of sediment as a source of phytosterol release in ASBs and highlights the importance of HRT and the PPW characteristics for predicting phytosterol fate in ASBs.

Changes in the organic character of post-coagulated Pinus radiata sulfite pulp mill wastewater under aerated stabilization basin treatment—A laboratory scale study

Treatment of wastewater from a Pinus radiata sulfite pulp and paper mill with coagulation followed by aerated stabilization basins (ASBs) was investigated to determine a treatment process that minimizes the colour formation. Two post-coagulation wastewaters were investigated, one low in P (Simulation A; BOD:N:P = 100:1.3:0.06) and the other higher in P but still moderately P-limited (Simulation B, BOD:N:P = 100:1.3:0.3). Changes in the organics character of the wastewaters were investigated at several stages of treatment: untreated, after coagulation; during and after ASB treatment, using HPSEC and solid-state 13C CP NMR spectroscopy. Effective reductions in colour 456nm, and UV 254 and 280nm, (∼80%) were achieved by coagulation using alum (1860 ppm). However, during ASB treatment, colour 456nm increased (>100%) in both simulations. HPSEC analysis showed that removal of HMW (>3000 Da) was achieved through coagulation with the simultaneous removal of LMW (<300 Da) in the ASB simulations. Subsequent to the removal of HMW and LMW, an increase of intermediate-range compounds (300–3000 Da) occurred. Solid-state 13C NMR analysis indicated some selective removal of aromatic and alkyl groups during the coagulation process and additional removal of aromatic C during ASB treatment. The slightly higher proportion of HMW (>1000 Da) in ‘A’ than ‘B’ and the slightly higher proportion of aromatic C and alkyl groups remaining in the effluent of ‘A’ might be the basis for differences in the colour development in the two ASB simulators. The low nutrient loading (external) in the pre-treated wastewaters has been shown to be sufficient to sustain microbiological growth of organisms that contribute to colour formation with ASB treatment. This occurred in both simulations and it was concluded that the manipulation of the BOD:N:P ratio to optimise BOD removal had little effect on colour removal. This paper provides insight on the nature of recalcitrant organic compounds causing colour formation.

Updating a model of pulp and paper wastewater treatment in a partial-mix aerated stabilization basin system

A relatively simple set of calculations was presented in 1994 to evaluate the effectiveness of each ASB cell as reactor, clarifier, and digester. The steady-state model, which incorporated estimates of solids settling and benthal feedback of BOD5 and nutrients, has been a reasonable diagnostic tool for municipal and industrial applications. Results have aided in understanding normal system function, the nature of chronic inefficiencies of individual systems, and appropriate modifications to meet changes in discharge requirements. For applications in the pulp and paper industry, several changes have been incorporated recently. Nitrogen limitation is not needed in modeling pulp and paper ASB reactions. Slowly biodegradable material is modeled as a contributor to soluble BOD5, and this contribution becomes a significant factor in the latter segments of an ASB. Phosphorus availability is modeled as a stoichiometric control of soluble BOD5 uptake. Anoxic microorganisms are assumed to be responsible for a portion of the soluble BOD5 consumption in the first ASB aeration zone. Finally, the long-term nutrient capture in ASBs is modeled as 3% for nitrogen and 28% for phosphorus.

Implications of Aerated Stabilization Basin Dredging on Potential Effluent Toxicity to Fish

Benthal solids accumulated in aerated stabilization basins (ASBs) must be dredged to regain treatment capacity. While dredging restores treatment performance, it has been associated occasionally with the failure to meet regulatory effluent toxicity limits at the time of dredging. A first study of its kind was undertaken to investigate the implications of ASB dredging on potential effluent toxicity to fish. The study showed that benthal solid slurry removed from the quiescent zone of an ASB with a hydraulic dredge was toxic to rainbow trout with a 96-hour median lethal concentration (LC50) of 2.2%. The high ammonia concentration in the sample was the main cause of fish mortality. Hydrogen sulfide and resin and fatty acids also were present in the dredged material at concentrations that could cause fish mortality. These findings have led to best management practices that can be used to mitigate or eliminate fish toxicity issues during dredging operations.

Aerated stabilization basin design and operating practices in the Canadian pulp and paper industry

Aerated stabilization basins (ASBs) currently account for about one third of the pulp and paper industry's secondary treatment capacity. We surveyed mills with ASBs to analyze design and operating practices. Of the 19 mills that responded, 15 were kraft, reflecting the industry's overall use of ASBs. Biochemical oxygen demand (BOD) and total suspended solids (TSS) loading to the ASBs varied considerably and were factors in biotreatment performance. Problems identified with some ASBs included excessive solids accumulation resulting in the need for frequent dredging, high TSS discharge, and difficulty with nutrient management. Most ASBs have either two or three cells. An important parameter identified for these cells is the benthal settling area. Too small an area results in a higher dredging frequency, with limited nutrient feedback. In general, ASB systems that used the most intensive mixing and aeration in the upstream cells tended to have a smaller benthal settling area, resulting in the need to dredge more frequently. Ideally, some benthal settling should be designed into the upstream cells to allow nutrient feedback where it is needed most. Key words: aeration tanks, lagoons, basins, aeration, benthic deposits, design, operations, biological treatment, primary treatment, tertiary treatment, nutrients, aerated stabilization basin (ASB).

Release of Contaminants from Melting Spray Ice of Industrial Wastewaters

This study was carried out to investigate organic and inorganic contaminant removal from melting spray ice produced from aerated stabilization basin treated pulp mill wastewater and the oil sands t...

OPTIMIZATION OF AN AERATED STABILIZATION BASIN PRETREATMENT SYSTEM AT A CORN AND POTATO CHIP PROCESSING PLANT

OPTIMIZATION OF AN AERATED STABILIZATION BASIN PRETREATMENT SYSTEM AT A CORN AND POTATO CHIP PROCESSING PLANTTom's Foods Inc. operates a corn and potato chip processing plant outside of Dallas, Texas. In order to meet pretreatment limitations, they operate an aerated stabilization basin (ASB) with preliminary treatment of food solids using vibratory screening and oil and grease (O&G) using a gravity separator. Recently, after increases in production, the ASB has had instances of elevated fixed...Author(s)Tom SandyInan BeydilliMike LucikRay SummersJack WardenSourceProceedings of the Water Environment FederationSubjectSession 3 Application of Membranes in IndustrialDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2003ISSN1938-6478SICI1938-6478(20030101)2003:2L.211;1-DOI10.2175/193864703784343875Volume / Issue2003 / 2Content sourceWEF EventFirst / last page(s)211 - 220Copyright2003Word count311

Ozonation of kraft pulp mill effluents: process dynamics

Pulp mill wastewater discharged from an aerated stabilization basin (ASB) of a kraft pulp mill was ozonated in an extra-coarse-bubble diffuser contactor. The ozonation process is dynamic. Therefore, modeling the reduction efficiencies of contaminants present in the pulp mill effluent and the ozone gas absorption process became more complex than the pure water situation. The ozonation-process-mitigated reduction of colour, absorbable organic halides (AOX), chemical oxygen demand (COD), and total organic carbon (TOC) were examined. Ozone was more effective in reducing the colour and AOX than in reducing the COD and TOC. At an ozone dose (ΔΔO3) of 230 mg L–1, the maximum reduction efficiencies of colour, AOX, COD, and TOC were 86, 44, 22, and 15%, respectively. Ozonation was also very effective in increasing the biochemical oxygen demand (BOD5) of the pulp mill effluent. The biochemical oxygen demand increased by about 320% at ΔΔO3 of 230 mg L–1. Ozone gas absorption dynamics were investigated by continuous monitoring of the feed-gas and off-gas ozone concentrations and flowrates. Owing to the occurrence of rapid reactions between ozone and some contaminants in the liquid phase, the mass transfer process was enhanced by an enhancement factor, E. The application of the well-known two-film theory and the assumption that the ozone reactions followed pseudo-first-order irreversible kinetics, the overall mass transfer coefficient, kLa, and the enhancement factor, E, were determined as functions of ΔΔO3. The induced reductions of pulp mill effluent contaminants and ozone gas absorption dynamics were compared to those obtained in other ozonation systems to investigate the effects of contactor design, configuration, operating conditions, and scale on the performance of the ozonation process. Key words: absorbable organic halides, chemical oxygen demand, colour, enhancement factor, mass transfer, ozonation process dynamics, total organic carbon.

Fate of resin acids in pulp mill secondary treatment systems

Profiles of resin and fatty acids (RFAs), COD, and aquatic toxicity were measured across the secondary treatment systems of three pulp mills. The RFAs sorb to suspended solids, principally fiber, and are partially removed through settling. An activated sludge system is more efficient in removing RFAs than an aerated stabilization basin (ASB) because of its higher solids level. Dehydroabietic acid accounts for a significant fraction of the effluent toxicity in the two ASBs studied. The microorganisms in an ASB are unable to respond rapidly to an RFA spill, and effluent toxicity can be elevated for a prolonged period because of hydraulic backmix. The applicability of several laboratory studies to field situations is assessed.

Maximizing the Enhanced Ozone Oxidation of Kraft Pulp Mill Effluents in an Impinging-Jet Bubble Column

An impinging-jet bubble column that utilized two venturi injectors has been tested for the ozone mass transfer applications in water and wastewater treatment. The venturi injectors were utilized to create turbulent gas-liquid jets in the ambient fluid. The injectors were placed at an intersecting angle of 125° and the distance between the centers of the nozzles was equal to 60 mm. The intersecting of the gas-liquid jets caused an increase in the turbulence produced in the liquid phase and therefore, maximized the gas-liquid mass transfer. Pulp mill wastewater discharged from an aerated stabilization basin (ASB) of a Kraft pulp mill was ozonated in the impinging-jet bubble column. The ASB pulp mill effluent was ozonated in a continuous-flow mode with and without re-circulation of the liquid effluent leaving the bubble column in order to determine the overall mass transfer coefficient (kLa) and the enhancement factor (E). The gas absorption dynamics and the ozonation process treatment efficiencies were investigated. The ozonation process was more effective in removing the color and AOX-causing compounds than COD and TOC and it caused the biodegradability of the pulp mill effluent to increase. Ozone gas absorption dynamics were studied by continuously monitoring the ozone feed-gas and off-gas concentrations and ozone feed-gas flowrate. Rapid reactions occurred between ozone and the contaminants in the liquid phase, and as a result, the mass transfer process was enhanced by an enhancement factor (E). The two-film theory was applied and by assuming that the ozone reactions followed pseudo-first order irreversible kinetics, the overall mass transfer coefficient and the enhancement factor were determined. During the initial stage of the ozonation process, higher enhanced overall mass transfer coefficients (EkLa's) were observed. As the ozonation proceeded, EkLa values decreased significantly as a result of die enhancement factor dependency on the operating conditions and the wastewater characteristics. The process off-gas dynamics in terms of the ozone off-gas concentrations and their dependency on the process operating conditions and the wastewater characteristics were also examined in order to investigate the ozone off-gas emissions’ dynamics during the ozonation of pulp mill effluents. Accurate and reliable predictions of these emissions will help achieve optimized designs and reliable process-control of the ozone off-gas destruction facilities.

Enhanced biological treatment of bleached kraft mill effluents — II. Reduction of mixed function oxygenase (MFO) induction in fish

Biological treatment studies with bleached kraft mill effluents (BKME) assessed the removal of hepatic MFO induction potency towards fish. Bench-scale activated sludge, facultative stabilization basin, and aerated stabilization basin processes were compared under conservative conditions of elevated sludge age and hydraulic retention times as well as moderate temperatures for the treatment of bleachery effluents from a modernized bleached kraft mill using oxygen delignification and 60% chlorine dioxide substitution. Optimized treatment for the removal of hard-to-degrade organics also consistently removed more than 85–90% of effluent-induced MFO activity of fish, based on laboratory bioassays. Follow-up mill-site pilot scale testing with an activated sludge treatment process in extended-aeration mode also demonstrated >90% reductions in the MFO induction potential of whole mill effluent. Characterization of various in-plant process waters sampled at the mill indicated that the softwood-line bleach plant was a major contributor (>70%) to the MFO induction potential of untreated and biologically-treated BKME.

Enhanced biological treatment of bleached kraft mill effluents — I. Removal of chlorinated organic compounds and toxicity

Laboratory-scale biological treatment studies with bleached kraft mill effluents assessed and optimized the removal of chlorinated organic compounds as well as aquatic and microbial toxicity. Three conventional biological processes, namely activated sludge and two stabilization basin treatment systems, were compared under conservative conditions of elevated sludge age (i.e. 15–25 days) and hydraulic retention times (i.e. 0.5–1 day and 15 days for the respective systems) as well as moderate temperatures for the treatment of softwood kraft bleachery effluents from a modernized mill using oxygen delignification and 60% chlorine dioxide substitution. Enhanced treatment performance was achieved with the optimized activated sludge, facultative stabilization basin and aerated stabilization basin processes as indicated by consistently high removals of conventional organic contaminants, polychlorinated phenolics (i.e. 85–93%), adsorbable organic halogen (i.e. 43–58%) and toxicity. The high level of polychlorinated phenolics removal was considered representative of an enhanced treatment capability for hard-to-degrade organics. The ultimate degree of biotreatability of various in-plant bleaching and non-bleaching process effluents from the kraft mill was also tested.

Tracing the Efficiency of Secondary Treatment Systems

A technique for mapping the three-dimensional performance of secondary treatment systems and for studying the behavior of specific compounds in-situ is described. [14C]Oleic acid was added to samples collected from various locations in the system. Each mixture was placed in a vial capped at both ends with semipermeable membranes, returned to its original position in the lagoon, and then retrieved after 1 day. The amount of radioactivity remaining, after cor rection for leakage and nonbiological losses, is a measure of biological activity. The approach revealed that water-column biodegradation was only one of many pathways for oleic acid removal, with sorption to solids also being important and, perhaps, dominant. Furthermore, it rationalized performance differences between an AST (activated sludge treatment) system and an ASB (aerated stabilization basin).

Nitrogen fixation in an aerated stabilization basin treating bleached kraft mill wastewater

Pulp and paper mill wastewaters normally contain very low concentrations of nitrogen, but many pulp mill aerated stabilization basin (ASB) treatment systems are operated with no supplemental nitrogen, while achieving high biochemical oxygen demand (BOD5) removal. A nutrient mass‐balance study, undertaken across one of the aerated lagoons in such an ASB system, found that a substantial input of nitrogen was occurring within this pond, amounting to approximately 600 kg nitrogen per day. Direct measurement of acetylene reduction (nitrogen fixation), both in the pond and in a laboratory simulation, showed that bacterial nitrogen fixation was responsible for the input of nitrogen. Most of the nitrogen for bacterial growth within the lagoon was supplied by atmospheric nitrogen fixation, and, consequently, nitrogen fixation was critical to overall system effectiveness. It appears that elevated dissolved oxygen concentrations may inhibit fixation. This may be an important constraint on the operation of such ASB systems, especially for the first lagoon, and represents a potential change to current thinking. The implications of bacterial nitrogen fixation, with respect to the effective operation and control of kraft mill ASB systems, are discussed.

Optimized design of wastewater treatment systems: Application to the mechanical pulp and paper industry: I. Design and cost relationships

AbstractFour different end‐of‐pipe waste‐treatment processes applicable to mechanical pulp and paper manufacture were modelled. Calculated costs for an average mill were capital $34–$44 million, operating cost $3.5–$6 million/year and discounted (10 years) $60–$85 million. Compared with mill reported values, capital and operating costs of activated sludge treatment (AST) were higher by 17 and 29%, respectively; those for aerated stabilization basin (ASB) were higher by 27 and 180%. Major variables affecting the costs were BOD and TSS levels and the wastewater‐to‐pulp ratio. It was concluded that ASB is more economical than AST and that anaerobic treatment plus AST could be advantageous at high BOD levels.

Biological nitrification of kraft wastewater

A program of batch, continuous-flow, and field pilot tests have been conducted to measure the extent and stability of nitrification in kraft wastewater. Laboratory batch tests measured the extent and rate of ammonia removal from kraft wastewater. Controlled variables included aerated stabilization basin (ASB) location, temperature, pH, ammonia concentration, black liquor content, bicarbonate content, and presence of acclimated nitrifying bacteria. Findings were that (a) moderate wastewater temperature (22-35°C), pH near 7.3, and black liquor spill control prevented slowing of nitrification, and (b) provision of acclimated nitrifying bacteria (by appropriate recirculation methods) dramatically reduced the residence time needed for nitrification in kraft ASBs. Laboratory-scale, fixed-film, continuous-flow tests were used to investigate dynamic responses to changes in wastewater composition and flow. Results demonstrated that the nitrifying films were not ‘damaged’ by 4- or 24-hour step increases in influent ammonia, but the films could not respond quickly enough to substantially dampen out the effect on effluent quality. A pilot 4-stage rotating biological contactor (RBC) was installed at an ASB to test the nitrification of kraft wastewater under actual process variations. The results during the 11-month run were: (a) the RBC demonstrated capability to consistently and substantially reduce NH4-N concentration below 1 mg/L, (b) about one month was needed to establish effective treatment, and (c) effective treatment was sustained at a maximum hydraulic loading rate of 0.11 m3/day per m2.

Practical experiences with aerobic biofilters in TMP (thermomechanical pulping), sulfite and fine paper mills in Canada

An industrial aerobic biofilter technology has been piloted extensively in Canada on several types of pulp and paper mill effluents, resulting in one full scale operational facility at one Canadian fine paper mill. In addition two industrial scale pilot plant tests were performed with the same technology, one in an integrated sulfite pulp and paper mill and one in a TMP mill. In the case of the fine paper mill, the full scale plant has two cells (8 m × 8 m × 6 m height of the media) and treats an unclarified but screened effluent with a loading of 3500 kg BOD/d. The system produces low quantities of biosludge (0.28 kg TSS/kg BOD removed), has a rapid rate of recovery after shock loadings and is very energy efficient (150 kW installed power for aeration). Pilot plant treatability studies were performed at one integrated Canadian sulfite mill using a combination of a biofilter-aerated lagoon system. The biofilter treated the most concentrated stream (sulfite pulp mill effluent) and this stream was then combined with the remaining wastewaters of the mill and polished in an aerated stabilization basin (ASB). The high quality ASB effluent (50 mg BOD/L/30 mg TSS/L) was non toxic to rainbow trout, Daphnia magna and photoluminescent bacteria. Integrated TMP mill effluents were treated in a 5 m3 aerobic biofilter filled with two types of media (10 to 20 mm and 20 to 30 mm). Under average loading conditions of 3.5 kg BOD/d.m3 media, the system produced effluents meeting regulation limits for BOD, TSS as well as for toxicity.