Laboratory modelling of manganese biofiltration using biofilms of Leptothrix discophora

Laboratory biofilters (pilot-scale, 20 l and laboratory-scale, 5l) were constructed in order to model the bioaccumulation of manganese (Mn) under flow conditions similar to those occurring in biofilters at groundwater treatment sites. The biofilters were operated as monocultures of Leptothrix discophora, the predominant organism in mature Mn oxidising biofilms. Biologically mediated Mn bioaccumulation was successfully modelled in both filter systems. The data obtained showed that in the small-scale biofilter, the Mn concentrations that gave the highest rate of Mn bioaccumulation, shortest maturation time, highest optical density (biomass) and growth rate were between 2000 and 3000 microg x l(-1). The non-problematic scale-up of the process from the laboratory-scale to the pilot-scale biofilter model suggests that Mn biofilters may be 'seeded' with laboratory grown cultures of L. discophora. By initially operating the biofilter as a re-circulating batch culture, with an initial Mn concentration of approximately 2500 microg x l(-1), it is hoped to reduce the filter maturation time from months to days.     

A comparison of media types in acetate fed expanded-bed anaerobic reactors

A synthetic feed, containing acetate as the only carbon source, was used to start-up four different anaerobic expanded-bed reactors containing three different types of microbial attachment media. The media types used were low-density anthracite, granular activated carbon (GAC) and two sizes of sand. All media types were of the same average diameter, 0.7 mm, except for a smaller sand, 0.35 mm. These media types were chosen to compare surface roughness, macroscopic shear stresses due to upflow velocity and sphericity. The 0.7 mm sand required the greatest upflow velocity, 16 cm/s, while the other reactors had upflow velocities of 5.5–6.0 cm/s. Sand had the least surface roughness and GAC had the roughest surface, while anthracite had the most angular shape. At steady-state, the GAC reactor retained 3.75–10 times the attached biomass retained on the other media tested and the GAC reactor accumulated biomass at a faster rate during start-up. Shear losses reflected the biomass accumulation with the two sand and anthracite media having shear loss coefficients 6–20 times greater than that of the GAC medium. Sand induced the formation of sludge granules in both sand reactors with two species of methanogens and stability of the sludge blankets was critical to reactor performance. Scanning electron microscopy demonstrated that attached growth developed in crevices where biomass was protected from shear forces. Attached growth on the sand and anthracite media was located only in crevices, while the GAC medium is completely covered with crevices and biofilm developed on the entire GAC particle. Surface roughness was critical to biofilm development with the rougher surface providing the better attachment medium.     

Cell wash-out and external mass transfer resistance in horizontal-flow anaerobic immobilized sludge reactor

Polyurethane foam has been studied as a support for anaerobic sludge immobilization in packed-bed bioreactors. Studies about fundamental aspects in reactors containing immobilized sludge in such a type of support must be carried out to permit simulation and optimization of their performance and to provide parameters for safe scale-up. The effect of the liquid superficial velocity on the wash-out of anaerobic biomass and the evaluation of the external mass transfer resistance are presented in this paper. The polyurethane foam cubic matrices were taken from a bench-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating kraft paper industry wastewater submitted to eight different water flow rates in a 10 ml tube segment for cell wash-out evaluation and six different glucose solution flow rates in a 10 ml differential reactor for external mass transfer resistance evaluation. There was a significant wash-out of total suspended solids (23%) but only 9% of volatile suspended solids were washed-out from polyurethane foam matrices when they were subjected to liquid superficial velocities ranging from 0.30 to 2.21 cm.s⁻¹. The external mass transfer resistance decreased with the increase in liquid superficial velocity, but the condition of minimum resistance was not obtained in the applied v_s range (0.007–0.075 cm.s⁻¹).     

Anaerobic treatment of fibreboard manufacturing wastewaters in a pilot scale hybrid usbf reactor.

The treatment of fibreboard manufacturing (FBM) wastewaters was carried out in an industrial pilot plant, which consisted of a hybrid upflow sludge bed filter (USBF) anaerobic reactor and a coagulation-flocculation unit as a pre-treatment. COD removal efficiencies of 90-93% were attained in the anaerobic reactor operating at 37degrees C at organic loading rates (OLR) of 6.5-8.5 kg COD/m3 d. Flocculant sludges were used as inoculum, and granulation was observed in the USBF reactor after 120 days of operation. The overall linear upward velocity (result of liquid and gas flow) was the key factor controlling biomass retention and, therefore, a stable operation at high OLR. According to ecotoxicity values (measured by means of bioluminescence assays), the wastewaters were partially detoxified, being EC50 values for the liquid effluent 25 times lower than those corresponding to the influent. Besides, phenolic compounds removal efficiencies of 90% were attained. The hybrid reactor configuration is an interesting alternative to treat these wastewaters since it is less sensitive to biomass clogging or floatation.     

Nitrification in tertiary trickling filters followed by deep-bed filters

Based on 20 months of pilot experiments, tertiary plastic media trickling filters have shown to be a feasible and cost-saving solution for the enlargement of existing treatment plants for nitrification. The influence of several process variables such as hydraulic load, media characteristics, NH₄-load, concentration fluctuations, suspended solids, organic nutrients and biomass grazing on nitrification activity was evaluated. From performance analysis along the trickling filter depth, basic design informations were obtained. In addition to suspended solids removal, subsequent deep-bed filtration proved to be an excellent final treatment to further reduce and stabilize effluent ammonia and nitrite residuals.     

Treatment performance of gravel filter media: implications for design and application of stormwater infiltration systems

Stormwater infiltration systems are widely used to address the flow and water quality impacts of urbanization. However, their pollutant removal performance is uncertain, with respect to varying filter depth, and over time. Seven simulation experiments were conducted on a laboratory-scale gravel infiltration system to test the pollutant removal under a range of water level regimes, including both constant and variable water levels. Gravel filters were found to be very effective for removal of sediment and heavy metals under all water level regimes, even as the system clogged over time. Despite the sediment particle size distribution being much smaller than the filter media pore size, sediment and its associated pollutants were effectively trapped in the top of the gravel filter, even when the water level was allowed to vary. A media depth of 0.5 m was found to achieve adequate pollutant removal. Breakthrough of pollutants may not be of concern, since physical clogging occurred first (thus determining the lifespan of the filter media). However, gravel filters were less effective at nutrient removal, particularly for dissolved nutrients.     

Biomass development in slow sand filters

Microbial biomass development in the sand and schmutzdecke layer was determined in two full-scale slow sand filters, operated with and without a light excluding cover. A standard chloroform fumigation-extraction technique was adapted to routinely measure microbial biomass concentrations in the sand beds. Sand was sampled to a depth of 10 cm and schmutzdecke was also collected at the same random positions on the uncovered filter. Interstitial microbial biomass in the uncovered sand bed increased with time and decreased with sampling depth. There was a small accumulation of sand biomass with time in the covered filter, but no relationship was apparent between biomass concentration and depth in this filter. Schmutzdecke did not develop on the covered filter and was spatially highly variable in the uncovered condition compared to the consistent patterns observed in interstitial biomass production. It is speculated that microbial biomass in the sand of uncovered filters is largely related to carbon inputs from photosynthetic activity in the schmutzdecke and involves mechanisms that spatially distribute carbon substrate from the schmutzdecke to the sand. However, total organic carbon and dissolved organic carbon removals were similar in both filters suggesting that relatively small biomass populations in covered filters are sufficient to remove residual labile carbon during advanced water treatment and little further advantage to water purification and organic carbon removal is gained by the increased production of biomass in uncovered slow sand filter beds.     

Assessing granular media filtration for the removal of chemical contaminants from wastewater

Granular media filtration was evaluated for the removal of a suite of chemical contaminants that can be found in wastewater. Laboratory- and pilot-scale sand and granular activated carbon (GAC) filters were trialled for their ability to remove atrazine, estrone (E1), 17α-ethynylestradiol (EE2), N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR) and N-nitrosodiethylamine (NDEA). In general, sand filtration was ineffective in removing the contaminants from a tertiary treated wastewater, with the exception of E1 and EE2, where efficient removals were observed after approximately 150 d. Batch degradation experiments confirmed that the removal of E1 was through biological activity, with a pseudo-first-order degradation rate constant of 7.4 × 10⁻³ h⁻¹. GAC filtration was initially able to effectively remove all contaminants; although removals decreased over time due to competition with other organics present in the water. The only exception was atrazine where removal remained consistently high throughout the experiment. Previously unreported differences were observed in the adsorption of the three nitrosamines, with the ease of removal following the trend, NDEA > NMOR > NDMA, consistent with their hydrophobic character. In most instances the removals from the pilot-scale filters were generally in agreement with the laboratory-scale filter, suggesting that there is potential in using laboratory-scale filters as monitoring tools to evaluate the performance of pilot- and possibly full-scale sand and GAC filters at wastewater treatment plants.     

Removal of heavy metals from storm and surface water by slow sand filtration: the importance of speciation

The removal of heavy metals from storm and surface waters by slow sand filtration is described. The importance of speciation as a technique for exploring and improving the mechanisms of removal is identified. Laboratory-scale slow sand filters operating at conventional flow rate and depth were shown to be able to reduce concentrations of selected heavy metals (Cu, Cr, Pb and Cd) found in road runoff, surface water and sewage effluents to drinking water standard. Nitrogen, volatile solids and modified Stover speciation were used to differentiate between the potential mechanisms of removal, i.e. active biomass, organic adsorption and simple adsorption or precipitation on the surface of the sand. The data presented show that adsorption via organic ligands was the predominant mechanism for metal removal at the surface of the filter but chemical adsorption was the more important deeper in the filter. In the lower layers the adsorbed metals were more easily exchanged than the organically bound metals. The precise chemical ligands were not identified and varied from metal to metal. The most important operational factors affecting performance were therefore the concentration of organic matter, filter depth and the flow velocity.     

Studies on the production of B. thuringiensis based biopesticides using wastewater sludge as a raw material

Growth and delta-endotoxin yield of Bacillus thuringiensis (Bt) subsp kurstaki in tryptic soy yeast extract (TSY) medium, soybean meal based commercial medium and wastewater sludge medium were studied. The viable spores (VS) count in sludge medium was comparable to that obtained in laboratory and commercial media. The entomotoxicity of the fermentation liquid (Bt grown sludge) against Choristoneura fumiferana was comparable to the concentrated commercial Bt formulation available in the market (Foray 48B). A higher entomotoxicity was observed in a sludge medium than in the TSY or soybean meal media. The secondary and mixed (mixture of primary and secondary) sludges from various wastewater treatment plants were also evaluated for spore formation and entomotoxicity yield. The VS count was higher in a mixed sludge compared to the secondary sludge at a similar sludge solids concentration. Both VS count and entomotoxicity yield was found to be a function of sludge solids concentration in the medium. The optimum value of solids concentration for Bt production was found to be 25 g (-1) (dry weight basis). Beyond this concentration, a drop in VS count and entomotoxicity yield was observed. A low C:N ratio in the secondary sludge and a high C:N ratio in the mixed sludge resulted in a higher entomotoxicity. The optimum value of C:N ratio in combined sludge for Bt production was found to be 7.9-9.9. Relationships between entomotoxicity and maximum specific growth as well as with specific sporulation rate were developed.     

An expert system for monitoring and diagnosis of anaerobic wastewater treatment plants

In this paper, an expert system (ES) developed for the monitoring and diagnosis of anaerobic wastewater treatment plants (AWT), is presented. The system was evaluated in a hybrid pilot plant of 1.1 m3 located in an industrial environment for the treatment of wastewaters from a fibreboard production factory. The reactor is a hybrid USBF, combining an upflow anaerobic sludge blanket (UASB) in the lower part and an upflow anaerobic filter (UAF) at the top.     

The effects of media size on the performance of biological aerated filters

Biological aerated filters (BAFs) are an attractive process option, particularly when low land usage is required. They can combine BOD, solids and ammoniacal nitrogen removal and can be utilised at both secondary and tertiary stages of wastewater treatment. Media selection is critical in the design and operation of BAFs to achieve effluent quality requirements. Two size ranges, 1.5-3.5 and 2.5-4.5 mm, of a foamed clay called StarLight C were used in pilot-scale reactors. Both performed well as BAF media, with reactor loads up to 12 kg COD m(-3) d and 4 kg suspended solids m(-3) d (based on working volumes). The most consistent effluent was obtained using the smaller medium since, at flow rates above 0.41 min(-1), the BAF using the larger medium produced an effluent containing more than 20 mg l(-1) of suspended solids for over 30 min after backwashing. Up to 70% longer run times, as determined by reaching a set head loss, were recorded for the BAF containing the larger rather than the smaller medium. Additionally, the development of pressure above the smaller medium filter bed tended to be logarithmic rather than linear. Reactor profiles indicated that suspended solids removal did not occur over the full 2.3 m depth of the columns. The BAF containing the smaller medium utilised a mean depth of 1.7 +/- 0.3 m, whereas a mean depth of 2.1 +/- 0.3 m was used by the larger medium BAF. Both the head loss development data and the suspended solids removal profiles indicated that the smaller medium BAF was underperforming as a filter.     

Estimating nitrifying biomass in drinking water filters for surface water treatment

The objective of this work is to estimate active nitrifying biomass and its main influencing factors in low-loaded biofilters based on operational data. An analytical approach based on balancing growth, decay and biomass removed by backwashing is proposed. The method is developed and applied in pilot-scale rapid sand filters for drinking water treatment. Decay rate was measured directly in the filter for different temperatures. To assess the amount of active biomass in backwash water, a technique based on respiration measurements was used. Backwash losses increased overproportional with balanced biomass in the filter. The impact of both parameters on active biomass is quantified exemplarily for a given constant nitrification rate.     

Trihalomethane Formation during Sludge Bulking Control with Chlorine

Effluent quality implications of bulking control with chlorine in activated-sludge treatment have been studied on laboratory scale. Batch chlorination of sludge samples led to the formation of trihalomethanes, mainly as chloroform (in hundreds of ùg/l) and even more non-specified organohalogens. Most organohalogens were formed from substances in the liquid effluent, and fewer out of the sludge solids. The presence of sludge lowered the concentration of extractable trihalomethanes in the effluent. Continuous chlorination in a laboratory-scale activated-sludge plant did not produce measurable quantities of any organohalogen compounds.     

Anaerobic codigestion of municipal solid waste and biosolids under various mixing conditions--I. Digester performance

The feasibility of codigestion of the organic fraction of municipal solid waste, primary sludge, and waste activated sludge was evaluated in mesophilic (37 degrees C), laboratory-scale digesters. In a first experiment, different startup strategies were compared using four digesters, operated under continuously mixed conditions. After two weeks, the experiment was continued under minimally mixed conditions. Results demonstrated that reducing the level of mixing improved digester performance. Therefore, in a second experiment, six digesters were operated to compare performance under continuous mixing and reduced mixing levels at various loading rates and solids levels. The continuously mixed digesters exhibited unstable performance at the higher loading rates, while the minimally mixed digesters performed well for all loading rates evaluated. In a third experiment, it was demonstrated that an unstable, continuously mixed digester was quickly stabilized by reducing the mixing level. These experiments confirmed that continuous mixing was not necessary for good performance and was inhibitory at higher loading rates. In addition, reduction of mixing levels may be used as an operational tool to stabilize unstable digesters.     

Performance of IFAS wastewater treatment processes for biological phosphorus removal

Integrated fixed film activated sludge (IFAS) is a promising process for the enhancement of nitrification and denitrification in conventional activated sludge systems that need to be upgraded for biological nutrient removal (BNR), particularly when they have space limitations or need modifications that will require large monetary expenses. Several studies have reported successful implementations of IFAS at temperate zone wastewater treatment facilities, typically by placement of fixed film media into aerobic zones. However, nearly all of the implementations have not included enhanced biological phosphorus removal (EBPR) in the upgraded systems. This is possibly because the treatment plants have been operated at low mixed liquor mean cell residence times (MCRTs), and EBPR would wash out of the systems at the low temperatures encountered, making it difficult to maintain EBPR. The primary objective of this study was to investigate the incorporation of EBPR into IFAS systems, and study the interactions between the fixed biomass and the mixed liquor suspended solids with respect to substrate competition and nutrient removal efficiencies. Three pilot-scale UCT/VIP configuration systems were used, one as a control and the other two with Bioweb media integrated into some of the anoxic and aerobic reactors. The systems were operated at different MCRTs, and influent COD/TP ratios, and with split influent flows. The experimental results confirmed that EBPR could be incorporated successfully into IFAS systems, but the redistribution of biomass resulting from the integration of fixed film media, and the competition of organic substrate between EBPR and denitrification would affect performances. Also, the integration of fixed film media into the anoxic reactors affected performances differently from media in aerobic reactors.     

Suspended solids abatement by pH increase—upgrading of an oxidation pond effluent

The effectiveness of solids abatement by pH increase was investigated using the jar test procedure with a bentonite tap water suspension and an urban wastewater and an oxidation pond effluent. The results indicated that, depending on the suspended particles and on the dissolved ions, pH values between 9.5 and 12 induced extensive solids elimination without adding any other chemical than a base, i.e. sodium hydroxide or lime. The major effective reactions are then the calcium carbonate precipitation and the magnesium hydroxide precipitation. Moreover, this process does not require a flocculation step but only a precipitation step where the particles are entrapped by sweep coagulation and adsorption—coagulation. A continuous reactor was operated with an oxidation pond effluent. A suspended solids concentration less than 30 mg/l was obtained by adjusting pH between 11 and 11.5 while the reactor was operated up to 20 m/h superficial upflow velocity corresponding to a residence time through the whole unit of 5 min only. The sludge settling velocity depends on pH and on the primary particles but a maximum settling velocity larger than 1 m/h is easily reached. The concentration factor is then about 100.     

循环造粒流化床处理水厂排泥水的试验研究

以西安市某自来水厂的沉淀池排泥水为处理对象,采用循环造粒流化床技术先进行工艺参数优化中试,再进行生产性试验研究。中试结果表明,循环造粒流化床的运行稳定性较高,即使进水浊度在200~800 NTU范围内变化或进水上升流速在25~70 cm/min之间变化,出水浊度仍可稳定保持在10 NTU以下;工艺优化参数如下:上升流速为70 cm/min,搅拌转速为5~8 r/min,助凝剂聚丙烯酰胺(PAM)投加量为4~5 mg/L。在中试的基础上进行生产性试验,出水浊度始终稳定在10 NTU以下,最佳间歇排泥间隔为4 h,出泥含水率为95.8%,处理成本为0.1元/m^3。中试及生产性试验结果表明,采用循环造粒流化床处理排泥水,具有出水水质好、抗冲击负荷能力强、污泥浓缩效果好、处理成本低等优点。     

饮用水生物强化过滤工艺生物膜特性研究

以水厂沉淀池出水为原水,对生物强化过滤工艺的生物膜形成过程进行了研究,探讨了不同滤料介质组成的生物滤柱的生物膜特性,分析了膜形成过程中污染物的去除效果和滤柱生物量的变化情况,并对膜形成过程的影响因素进行了讨论.结果表明,在活性炭-石英砂滤料上生物膜形成效果要优于无烟煤-石英砂双层滤料和石英砂单层滤料;反冲洗水含氯对生物膜形成有负面影响,对无烟煤-石英砂滤柱的影响尤为显著;可以CODMn和NO-2的去除率作为生物膜成熟的评价指标.     

The Buoyant Filter Bioreactor: a high-rate anaerobic reactor for complex wastewater--process dynamics with dairy effluent

A novel high-rate anaerobic reactor, called "Buoyant Filter Bioreactor" (BFBR), has been developed for treating lipid-rich complex wastewater. The BFBR is able to decouple the biomass and insoluble COD retention time from the hydraulic retention time by means of a granular filter bed made of buoyant polystyrene beads. Filter clogging is prevented by an automatic backwash driven by biogas release, which fluidizes the granular filter bed in a downward direction. During filter backwash, the solids captured in the filter are reintroduced into the reaction zone of the reactor. The reaction zone is provided with a mixing system, which is independent of the hydraulic retention time. The performance of a laboratory-scale BFBR was studied for the treatment of dairy effluent, chosen as a model complex wastewater. The dairy effluent was not pre-treated for fat removal. The BFBR was operated over 400 d and showed greater than 85% COD removal at 10 kg COD/(m3/d). The COD conversion to methane in the BFBR was essentially complete. The BFBR performance improved with age, and with feed containing 3200 mg COD/l, the treated effluent had 120 mg COD/l and no turbidity. The hold-up of degradable biosolids, including scum, inside the BFBR was estimated using starvation tests. When load is increased, scum accumulates inside the BFBR and then decays after undergoing change from hydrophobic to hydrophilic. This is explained as the accumulation of fat solids, its conversion to insoluble long chain fatty acids and its further solubilization and degradation.