Secondary Treatment Systems Research Articles

Performance of floating and sunken media biological aerated filters under unsteady state conditions

The biological aerated filter (BAF) combines both biological treatment and solids removal in one submerged, aerated three phase reactor. Over the last 20 yr biological aerated filters have been developed not only as competitors for other secondary treatment systems such as trickling filters and activated sludge plants but also as tertiary treatment systems. The aim of this work was to compare the performance of two such reactors, one containing a floating media and the other containing a sunken media under identical conditions during start-up and with increasing hydraulic flowrates. Two methods of start-up were used. The first method used activated sludge as seed which was recycled through the reactor, the second method involved simply passing the process liquid (settled domestic sewage) through the reactor at the initial flowrate. Following a period of steady-state the flowrates were increased incrementally and the performance of the reactors analysed during and after each increase. The results for the start-up indicated that the overall time to reach steady-state using both methods was approximately the same but due to the initial time required for the recycling of the activated sludge, this method took slightly longer. From an initial start-up loading of 0.486 kg m −3 d −1 (SS) and 0.568 kg m −3 d −1 (sCOD) suspended solids and soluble chemical oxygen demand removal efficiencies dropped to below 50% when loadings of 1.397 kg m −3 d −1 (SS) and 1.403 kg m −3 d −1 (sCOD) were reached. The floating media performed better at the higher flowrates under shock loading conditions than the sunken media.

Design of a hybrid reed bed system to achieve complete nitrification and denitrification of domestic sewage

The design of vertical-flow (VF) reed beds is reviewed and the performance of the few worldwide existing hybrid systems, combining both horizontal- and vertical-flow beds, is assessed. Horizontal-flow (HF) beds are good for suspended solids removal and will remove BOD5 up to a set loading. Vertical-flow beds can achieve BOD5 removal at much higher loading rates and they are capable of complete nitrification as tertiary or secondary treatment systems. It is possible to achieve biological denitrification in horizontal-flow beds. By combining horizontal- and vertical-flow systems in the appropriate process sequence it is thus possible to produce a system which removes BOD5, TSS and achieves complete nitrification as well as substantial removal of nitrate and hence a lowered Total N.The paper discusses the possible process options for combining horizontal- and vertical-flow systems. One example of these systems will be described in more detail. This is a flexible hybrid system being built by Severn Trent Water. Designed to treat the flow for a small village with a population of 129 it will have vertical-flow beds followed by horizontal-flow beds. The design allows for flexibility such that the size of the vertical-flow and horizontal-flow stages can be altered (for experimental purposes) to allow the design arrangement to be stressed and performance evaluated with the intention of defining the optimum loading rates for each of the stages.The same site also has sludge drying reed beds for treating the primary sludge.

An overview of recent studies on the potential of pulp‐mill effluents to alter reproductive parameters in fish

In the early 1990s, many Canadian pulp and paper mills implemented process changes to comply with new regulations that came into effect in 1993. These regulations placed stricter guidelines on a number of parameters in effluent discharges, including limits on acute toxicity, on the discharges of suspended solids, and on biochemical oxygen demand. To meet these new regulations, many of the older Canadian pulp and paper mills had to install secondary treatment systems. The investment by the Canadian pulp and paper industry was in excess of $5 billion, and the implementation of the new regulations and the process changes took several years. The new regulations were an extension of regulations designed in the early 1970s and were not designed specifically to address the reproductive responses recently reported in fish collected downstream of mills in Scandinavia and North America. This report describes a series of projects conducted between 1991 and 1996 to evaluate the effectiveness of the new regulations to address the issue of reproductive responses in fish associated with exposure to pulp‐mill effluents. These studies have shown that the existing short‐term bioassays do not adequately predict the potential of effluents to affect reproduction in wild fish. Laboratory testing using fathead minnows exposed over a full life cycle confirmed depression in sex steroid production, delay in sexual maturity, reduced egg production, and changes in secondary sex characteristics documented at some sites. Our studies demonstrated that both steroid hormone changes and induction of liver detoxification enzymes take place quickly. While short‐term exposures can predict the potential of some effluents to impact steroid hormone production, there is no readily available assay that can be widely applied. In the absence of a usable and transferable laboratory bioassay, field collections were conducted at a number of sites. Generalizations are not possible at this time, but impacts have been seen at a variety of sites, and partial recovery has been documented at five sites in North America following various process and waste treatment changes. Data gaps and critical research areas are identified.

A simplified modeling approach using microbial growth kinetics for predicting exposure concentrations of organic chemicals in treated wastewater effluents

Various mathematical relationships have been used to assess exposure concentrations of organic chemicals when emissions occur via wastewater treatment. These relationships range from a simple removal factor calculation to more sophisticated approaches using kinetic based mathematical models. While these existing approaches have been used by decision makers to screen new chemicals for exposure assessments, they all have limitations in the predictive capabilities. Thus, a simplified modeling approach grounded in sound scientific fundamentals that utilizes relatively easy to obtain input parameters is needed. In this paper a simplified modeling approach that utilizes microbial growth kinetics was developed for predicting effluent concentrations in secondary biological wastewater treatment systems. Receiving water predicted exposure concentrations (PEC) are assessed by using a dilution factor. One advantage of this approach is that it allows for wastewater treatment plant effluent concentrations, and therefore receiving water exposure levels, to be predicted with a minimum amount of experimental data. It also provides quantitative data that can be used to assess the relative biodegradability of different chemicals for use in regulatory and risk assessment activities.

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).

In-Situ Measurement of Local Biodegradation during Secondary Treatment: Application to Bleached Pulp Mill Chloroorganics

A procedure has been developed for tracing the biodegradation of effluent constituents in the water column of secondary treatment systems and applied to chlorinated bleach plant components. Pulp is bleached with radioactive [36Cl] Cl2 or ClO2 to give labeled AOX. Next, samples are drawn from various locations and depths in the treatment system, and the labeled AOX is added to each sample. The amended samples are transferred to vials capped at both ends with semi-permeable membranes. These hold the microorganisms and prevent most of the tagged AOX from diffusing out, but allow the flow of dissolved oxygen and nutrients. The vials are then inserted into a sampler at 1-ft depth intervals, which is placed in the treatment system for a period equal to the hydraulic retention time of the lagoon. Thus, the radioactive AOX experiences the conditions prevalent in the lagoon while being held captive inside the vial. After retrieval of the sampler, the radioactivity remaining in each vial is determined, and the remo...

Time, sunlight, and the fate of biotreated kraft mill organochlorines (AOX) in nature

A system of gas- and light-permeable sealed sample bags was employed to monitor the fate and persistence of the color and organochlorines (AOX) exiting the secondary treatment systems of three modern pulp and paper kraft mills. Placed in a remote lake at various depths, the bags of effluent showed that the “stable” biotreated AOX from elemental chlorine-free bleaching was largely but not completely mineralized in 4 months, largely by sunlight-dependent processes. Mill AOX and color was partially protected from photomineralization by natural organic matter (NOM) in the water. Effluent chromophores were more rapidly and completely degraded by light than AOX, and neither AOX nor color were very susceptible to biological degradation. The biotreated effluents, even when undiluted, were not acutely toxic and over time gave rise to diverse, flourishing microalgal, protozoan, and metazoan communities in the sealed bags. Thus these concentrated effluents apparently had no acute or chronic toxicity for a diverse assemblage of aquatic organisms over a 4-month period.

Experience with establishment and operation of reed bed treatment for small communities in the UK

The design and development of constructed reed beds for secondary, tertiary and storm outflow treatment is described from the experience of a major water utility in the Midland region of the UK. There were only two trial sites in 1987, but 125 sites by June 1995. The problems and their resolution with the establishment ofPhragmites in gravel filled beds are described. Two secondary treatment systems with horizontal subsurface flow beds arranged in terraces show that dilute sewage can be treated to a good secondary standard, but that nitrification is likely to be only partially complete. The example of four tertiary treatment applications showed that, for beds sized at 0.7 to 1.2 m2/pe, effluents consistently averaged better than 5 mg/l BOD5 and 10 mg/l TSS. Three sites showed improved removal of ammonium nitrogen (N) after the first year, with better than 50% removal. One site, treating highly nitrified secondary effluent, showed a small net increase in ammonium-N even after 4 years. Samples taken by the regulatory authority from 79 sites confirm the ability of the system to meet tight standards for BOD5. A comparison made of the performance of storm reed beds during three storm events showed relatively consistent removal of BOD, TSS, ammonia nitrogen and TON.

A dynamic solids inventory model for activated sludge systems

Clarifier hydrodynamics plays an important role in the activated sludge process. Attention has long been focused on the biological behavior of the aeration basin in the secondary treatment system. One-dimensional settler models or empirical relationships have typically been coupled in wastewater treatment plant simulation systems to represent the clarifier. The research on the hydrodynamic aspects of the process are currently restricted to a clarifier uncoupled from the aeration basin. In this paper, a dynamic model of the activated sludge process is presented in which balanced emphasis is put on the hydrodynamic aspect of the system. The model integrates a biological reaction submodel for an aeration basin with a two-dimensional hydrodynamic solids transport submodel for the secondary clarifier. A verification of the model is carried out against a set of field data and shows good agreement. The model has been used to investigate the response and the interdependency of the aerator and clarifier in the activated sludge system.

Aerated Anoxic Oxidation-Denitrification Process

The conventional practice for an anoxic denitrification basin has been to minimize oxygen input on the basis that it is detrimental to the process. For existing secondary treatment systems, allotting 25–35% of the aeration volume for an unaerated anoxic zone will significantly reduce plant capacity. Further, a group has held that bulking sludge control is best achieved by eliminating all forms of oxygen, including nitrates, from the initial contact or biological selector zones. The 6.75 m 3 /s Phoenix 91st Avenue wastewater-treatment plant (WWTP) was designed with nitrate recycle to the selector zones for bulking sludge control and the anoxic zones were provided with fine-bubble diffusers to increase oxidation capacity while simultaneously removing the recycled nitrates. This paper provides the process, design rationale, plant-layout features, plant modifications to existing structures, and the operating results for the facility. The successful performance of the 1.3 m 3 /s prototype plant resulted in the initiation of the design for conversion of the other four plants, totaling 5.4 m 3 /s capacity, to the aerated anoxic design.

Biosorption of high molecular weight organochlorines in pulp mill effluent

Since biosorption is considered an important step in the removal of organochlorines in secondary treatment systems from pulp and paper mill effluent, the role of biosorption in the removal of high molecular weight organochlorine (HMW AOX) was studied. Ultrafiltered (> 1000 Da) total mill effluent was used as the sorbate and municipal sewage sludge as the sorbent. Eight different parameters were tested: contact time, cell viability, cell concentration, sorbate concentration, desorption, cell type, sorbate type and temperature. Biosorption equilibrium was reached in the first 30 min of an experiment and the removal of the high molecular weight organochlorine was independent of cell viability. The biosorption was characterized by the Freundlich isotherm [ Q ( mg/g VSS) = KC I n , C + AOX concentration (mg/l) ]; the observed values for the Freundlich coefficients K and l/ n were 1.83 and 0.53, respectively. The Langmuir isotherm [ Q = 7.5 c/(3.2 + C)] provided a better characterization for biosorption of HMW AOX since it predicted a saturation biomass phase concentration of 7.5 mg Cl/g VSS at high AOX concentrations. The maximum percentage removal of HMW AOX was 70% at a biomass concentration of 2.0 g VSS/l or higher. About 8% of the organochlorines desorbed from live biomass after 24 h indicating that the process is not readily reversible. Based on the experiments at various temperatures, the enthalpy of sorption was found to be −4 kJ/mol Cl.

USING WATER HYACINTH TO TREAT MUNICIPAL WASTEWATER IN THE DESERT SOUTHWEST1

ABSTRACT: Water hyacinth (Eichhornia crassipes L.) has shown to be effective in the treatment of municipal wastewater in a pilot study begun in January 1989 by the Pima County Wastewater Management Department and researchers associated with The University of Arizona's Office of Arid Lands Studies in the Sonoran Desert near Tucson. The influent pumped into the pilot facility's six raceways (ponds) typically has been treated secondary effluent diverted from a conventional treatment facility, although primary effluent from the same facility also has been treated. The Secondary Influent Treatment System has met the Arizona Department of Environmental Quality (ADEQ) tertiary standard for BOD5 and TSS of 10 mg/l for every month of its operation since March 1990; the Primary Influent Treatment System met the ADEQ secondary standard for BOD5 and TSS of 30 mg/1 for most of the 10 months it was in operation.

Aerated Anoxic Biological NdeN Process

The conventional practice for an anoxic denitrification basin has been to minimize oxygen input on the basis that it is detrimental to the process. For existing secondary treatment systems, allotting 25-35% of the aeration volume for an unaerated anoxic zone will significantly reduce plant capacity. Further, one group has held that bulking control is best achieved by eliminating all forms of oxygen from the initial contact or biological selector zones. The Phoenix 91st Avenue WWTP was designed with nitrate recycle to aerated selector zones and the anoxic zones were provided with a dense array of fine bubble diffusers. The prototype NdeN process was able to maintain the 1.31 m3/s secondary capacity with aerated anoxic zone receiving 20-25% of the total airflow. Net sludge yields were 30-50% higher than anticipated due to primary clarifier solids losses at higher flows which reduced SRTT to ≤ 5 days. At 5.0-5.5 day SRTT, effluent averaged 8.3 mg/L TN, 1.75 mg/L NH4N and 5.7 mg/L NO3N. Nitrobacter N oxidation rates were unexplainably lower than the Nitrosomonas N oxidation rates causing effluent NO2N.

Response of hepatic mfo activity and plasma sex steroids to secondary treatment of bleached kraft pulp mill effluent and mill shutdown

AbstractThe discharge of bleached kraft mill effluent (BKME) into Jackfish Bay, Lake Superior, Canada, has been associated with a number of changes in the physiology and whole organism responses of four fish species. Current studies have been following physiological indicators of BKME impact for evidence of improvement after the installation of a secondary treatment system. Secondary treatment has not been successful in eliminating BKME impacts on hepatic mixed‐function oxygenase (MFO) activity in white sucker (Catostomus commersoni) because fish collected from Jackfish Bay after initiation of secondary treatment exhibited similar MFO activity as recorded in samples collected during two previous years. Hepatic MFO activity was also induced in long‐nose sucker (Catostomus catostomus), lake whitefish (Coregonus clupeaformis), and lake trout (Salvelinus namaycush) after secondary treatment. However, samples collected two weeks after a planned mill maintenance shutdown showed no MFO induction in long‐nose sucker, reduced MFO activity in white sucker, and a reduced impact zone for MFO induction in lake whitefish. A reduction in circulating levels of gonadal sex steroids has also been recorded in fish exposed to primary‐treated BKME in Jackfish Bay. In contrast, neither secondary treatment nor mill shutdown was sucessful in eliminating impacts of BKME exposur on levels of testosterone and 17β‐estradiol in female white sucker and long‐nose sucker. The short duration of MFO induction after shutdown and the peristence of steroid reductions suggest that (a) secondary treatment has not been successful in removing “MFO‐active” compounds from BKME, (b) induction is not related to sediment contamination with persistent compounds, (c) the inducing agents are rapidly cleared by fish, and (d) effects on steroids may not be directly related to MFO induction.

Comprehensive Study of a Bleached Kraft Mill Aerobic Secondary Treatment System

Abstract A comprehensive study (physical, chemical and biological parameters) was made of a conventional secondary treatment system (aeration stabilization basin) linked to a state-of-the-art bleached kraft mill. Overall the system removed 88% of the BOD, 62% of the COD, 47% of the TOC, 56% of the AOX and 69% of the suspended solids present in the influent stream. Of the total removed, the first aeration cell was the most active area of the system, responsible for the removal of 70% of the BOD5, 57% of the COD, 43% of the TOC, 75% of the AOX, and all of the acute toxicity entering the system. Cell 2 was found to be carbon limited. Unlike Cell 1, Cell 2 played a significant role in suspended solids removal.

Changes in Maturity, Plasma Sex Steroid Levels, Hepatic Mixed-Function Oxygenase Activity, and the Presence of External Lesions in Lake Whitefish (Coregonus clupeaformis) Exposed to Bleached Kraft Mill Effluent

Lake whitefish (Coregonus clupeaformis) exposed to primary treated bleached kraft mill effluent (BKME) had reduced gonadal development and increased liver size relative to two reference populations. These results parallel our previous work on the white sucker (Catostomus commersoni) exposed to BKME at the same Lake Superior site. More detailed studies conducted in 1990, after the installation of an aeration stabilization basin at the pulp mill, found that lake whitefish exhibited reduced gonad sizes, delayed age to maturation, decreased levels of the plasma sex steroids testosterone and 17β-estradiol, and elevated hepatic mixed-function oxygenase (MFO) activity. Liver size was smaller following operation of the secondary treatment system. More than 20% of the lake whitefish collected at the BKME site in 1990 exhibited lateral, slash-like lesions which penetrated the body cavity. Histological examination revealed no evidence of an infectious etiology, and the wounds could not be accounted for by known causes. Similar lesions were found in 1991 near a second BKME discharge.

Innovative management of an Aerated/Facultative Lagoon suspended—growth biological treatment system for high strength industrial waste stabilization

AbstractCoors Bio Technology Products Company, in Johnstown, CO is a subsidiary company of Adolph Coors Brewery Company in Golden, CO. Coors BioTech is a corn wet–milling industrial plant which processes shelled corn and converts it into several basic economical products: high fructose corn syrup (HFCS), corn oils, starch, sugars, and various agricultural by–products (Figure 1). The corn wet–milling operation and HFCS refining process generates a continual discharge of numerous process wastes. This wastewater is characterized as being a high strength, soluble, biodegradable waste, highly variable in composition. Coors BioTech treats their own industrial waste on site at their wastewater treatment plant using the activated sludge process. The objective of this paper is to provide a more complete understanding of the necessity for innovative management of the Aerated/Facultative Lagoon in the Coors BioTech waste treatment process, and suggest the applications of such lagoons in secondary biological treatment systems for high strength industrial waste stabilization [1–5].

Utilization of created wetlands to upgrade small municipal wastewater treatment systems

Created wetlands offer a low cost, low maintenance, and practical alternative for upgrading secondary municipal wastewater treatment systems. The removal efficiencies, effects of seasonal temperature variations, and effects of increased loading rates on contaminant removal within such a system was studied by Auburn University researchers at a created wetland site in Hurtsboro, Alabama. The 0.16 ha system consisted of a two cell wetlands planted with cattails (Typha latifolia), bulrush (Scirpus validus), arrow duck potatoes (Sagitaria latifolis), burr reeds (Spargaminum eurycarpun), water pennywort (Hydrocotyl ranunculoides), and parrotfeather (Myriophyllum brasiliense). Testing occurred from January through September of 1988 at hydraulic loading rates of 169, 289, and 345 m3 ha−1 d−1. The monthly average total suspended solids influent: effluent mg L−1 concentration ratio during the study period was 135:19 while the monthly average total BOD5 influent: effluent mg L−1 concentration ratio was 38:8. Once the system stabilized, the monthly average total BOD5 effluent concentration remained essentially constant over the range of average BOD5 loading rates employed in this study. Total Kjeldahl N removal was more effective at loading rates of 2.6 kg ha−1 d−1. The monthly average influent: effluent TKN mg L−1 concentration ratio was 15:4.

Optimization Techniques for Secondary Wastewater Treatment System

Optimization approaches are shown to be effective in solving a comprehensive model of an activated sludge wastewater treatment system. A new decomposition approach tailored to take advantage of the special structure of the treatment system is presented. A liquid subsystem and a sludge subsystem are specified, and a series of subproblems is solved. Coordination of the solutions is then required. A widely used nonlinear programming algorithm (GRG2) and a geometric programming algorithm (IGGP) designed to handle equality constraints are also demonstrated. Each of the approaches is shown to produce efficient solutions for a test problem; computational requirements are similar. The first approach most clearly illustrates cost‐effective trends and alternative solutions, while the third is most straightforward. The availability of the different approaches is important because one may be more suitable than the others for a particular application—especially if the model has been modified or extended.

A review of the technological feasibility of aquacultures for municipal wastewater treatment

The technical feasibility of utilising aquacultures for municipal wastewater treatment is reviewed. Aquacultures containing one or more aquatic weeds are cost effective for secondary and tertiary wastewater treatment, compared to the highly energy intensive conventional secondary and tertiary wastewater treatment systems. The major advantages are less capital and maintenance costs required as opposed to conventional wastewater treatment. Aquatic treatment systems utilising one or two aquatic weeds are efficient in substantial removal of phosphorus and nitrogen from the wastewater compared to the conventional secondary and tertiary wastewater treatment systems. Further, biogas generated from the harvested aquatic weed biomass could meet the treatment costs of the aquatic treatment systems utilising these aquatic weeds. Year round treatment of municipal wastewater utilising these aquatic weeds is possible even in the temperate regions of the world by housing the treatment systems in green houses. Other aqua...