Effect of iron hydroxide on the phosphate elimination during anaerobic digestion of active sludge

Addition of iron (III) hydroxide during methanogenic digestion of active sludge by anaerobic sludge displaying an iron-reducing activity resulted in a microbial reduction of iron (III) with formation of iron (II), capable of precipitating phosphates. Feasibility of eliminating 66.6 to 99.6% of dissolved phosphate at initial concentrations of 1000 to 3500 mg PO4(3-)/l by adding 6420 mg/l iron (III) hydroxide into a reactor for anaerobic fermentation of active sludge. The optimal ratio of iron (III) added to dissolved phosphate eliminated (mg) providing a 95% elimination amounted to 2:1. These results may be used in a new technology for anaerobic wastewater treatment with phosphate elimination.     

Phosphate removal from the returned liquor of municipal wastewater treatment plant using iron-reducing bacteria

AIM: The application of iron-reducing bacteria (IRB) to phosphate removal from returned liquor (liquid fraction after activated sludge digestion and anaerobic sludge dewatering) of municipal wastewater treatment plant (WWTP) was studied. METHODS AND RESULTS: An enrichment culture and two pure cultures of IRB, Stenotrophomonas maltophilia BK and Brachymonas denitrificans MK identified by 16S rRNA gene sequencing, were produced using returned liquor from a municipal WWTP as carbon and energy source, and iron hydroxide as oxidant. The final concentration of phosphate increased from 70 to 90 mg l(-1) in the control and decreased from 70 to 1 mg l(-1) in the experiment. The mass ratio of removed P to produced Fe(II) was 0.17 g P g(-1) Fe(II). The strain S. maltophilia BK showed the ability to reduce Fe(III) using such xenobiotics as diphenylamine, m-cresol, 2,4-dichlorphenol and p-phenylphenol as sole sources of carbon under anaerobic conditions. CONCLUSIONS: Bacterial reduction of ferric hydroxide enhanced the phosphate removal from the returned liquor. SIGNIFICANCE AND IMPACT OF THE STUDY: The ability of the facultative anaerobes S. maltophilia BK and B. denitrificans MK to reduce Fe(III) was shown. These micro-organisms can be used for anaerobic removal of phosphate and xenobiotics by bacterial reduction of ferric ions.     

Inhibition of methanogenesis from acetate by Cr+3 and ammonia

Summary 4000 mg/l of N–NH₄ ⁺ and 12 mg/l or Cr⁺³ caused a 50% reduction in aceticlastic methanogenic activity of an anaerobic sludge.Methanosarcina-like andMethanothrix-like cells were differently affected by the toxicants. The inhibition caused by Cr⁺³ was reverted by its removal, by addition of iron and by increasing the biomass.     

Removal of phosphate in a sequencing batch reactor by Staphylococcus auricularis

A sequencing batch reactor (SBR) was used to remove phosphate in biological wastewater treatment as an alternative to the activated sludge process, in order to improve the low removal efficiency of phosphate and the operational instability. After a cycle of 2 h anaerobic and 4 h aerobic conditions, phosphate removal was optimized. The removal efficiencies of 5 and 50 mg phosphate l^–1 by Staphylococcus auricularis under repeated anaerobic and aerobic conditions were above 90%. These results showed that a long adaptation time, one of the major problems in biological phosphate removal process, was overcome by SBR.     

The effect of various iron hydroxide concentrations on the anaerobic fermentation of sulfate-containing model wastewater

The addition of iron hydroxide and iron-reducing bacteria into a reactor for anaerobic processing of sulfate-containing wastewater was shown to decrease sulfate reduction and sulfide concentration, while increasing the total organic carbon (TOC) and methane production. The effect of iron (III) in sulfate-containing wastewater depended on its dose, which can be expressed as molar ratio Fe(III)/SO ₄ ^2? . Sulfide concentration increased monotonically, reaching 91 and 45 mg/l after 15 days of processing at Fe(III)/SO ₄ ^2? ratios of 0.06 and 0.5, respectively. However, soluble sulfide production was not observed at ratios equaling 1 and 2. At ratios of 0.06, 0.5, 1, and 2, the maximum rates of TOC removal were 0.75, 1.15, 1.39, and 1.55 g TOC/g of organic matter (OM) per 1 h. Methane production rates were 0.039, 0.047, 0.064, and 0.069 ml/g OM per 1 h, with the mean relative amounts of methane in the biogas being equal to 25, 41, 55, and 62%, respectively. These data can be applied to the development of new methods of anaerobic purification of sulfate-containing wastewater.     

Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process

The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn²⁺ and Cd²⁺ ions, and complete removal was achieved even at 20 mg Zn²⁺/l and 20 mg Cd²⁺/l. However, with over 1 mg Cu²⁺/1 TOC removal efficiency decreased. PO _inf4 ^sup3- removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn²⁺/l and 1 mg Cd²⁺/l. Higher concentrations adversely affected PO _inf4 ^sup3- removal. Copper again proved detrimental; no PO _inf4 ^sup3- removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO _inf4 ^sup3- to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan.     

A novel membrane bioreactor enhanced by effective microorganisms for the treatment of domestic wastewater

The activated sludge membrane bioreactor (MBR) has been shown to have some advantages for the processing and reclamation of domestic wastewater. We hypothesized that certain microorganisms, chosen for their abilities to decompose the chemical components of raw sewage, would, when coupled with the MBR, significantly improve the stability and efficiency of this system. We selected environmental bacterial strains which oxidize ammonia and nitrites and produce protease, amylase, and cellulase for the development and testing of a novel biologically enhanced MBR (eMBR). We compared the eMBR with the activated sludge MBR. With the eMBR, the average values of effluent quality were: chemical oxygen demand (COD), 40 mg/l(average efficiency of removal 90.0%); and NH₄ ⁺–N, 0.66 mg/l(average efficiency of removal 99.4%). Effluent qualities met the standard and were stable during the entire 90 days of this study. For the activated sludge MBR, the COD removal rate was 91.7%, and the NH₄ ⁺–N removal (94.8%) was less than that of the eMBR. Start-up time for the eMBR was only 24–48 h, much shorter than the 7–8 days required to initiate function of the standard MBR. The biomass concentrations of total heterotrophic bacteria and autotrophic bacteria in the eMBR did not fluctuate significantly during the course of the study. Various kinds of microorganisms will establish an ecological balance in the reactor. Compared with the activated sludge MBR, the eMBR not only produced an excellent and stable quality of effluent but also resulted in a shorter time to start-up and significantly improved the efficiency of NH₄ ⁺–N removal.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.     

Biodegradation of coal slurry transport wastewater organics

Summary Activated sludge was successful in reducing the levels of dissolved organic carbon (DOC) in coal slurry wastewaters. DOC removal by the activated sludge ranged from 61% to 97% with a large percentage (21–41%) of this DOC being completely metabolized to CO₂. Second order kinetic constants (k ₂) developed for DOC removal ranged from 1.39·10^–4 to 2.30·10^–1 liter·day^–1·(mg of sludge)^–1, providing evidence that biological treatment was an effective mechanism for reducing the pollution potential of the slurry wastewaters. After treatment with activated sludge a residual DOC remained in the wastewater and data from ultrafiltration studies indicated that this residual carbon was of MW>1000. The activated sludge preferentially removed the lower (MW<1000) molecular weight compounds and the higher molecular weight DOC was more resistant to biological attack. However, extended acclimation (greater than 1 month) enabled the activated sludge to remove the higher molecular weight DOC from the slurry wastewaters.     

The Role of Particulate Organic Matter and Acetic Acid in the Removal of Phosphate in Anaerobic/Aerobic Activated Sludge Processes

Acetic acid is thought to be an important substrate for the removal of phosphate in anaerobic/aerobic activated sludge (AS) processes. However, the acetic acid content in municipal sewage is low, and the main organic compounds in such sewage are particulate organic matters (POM) that are converted to endogenous substrates (E(ntrapped) POM, i.e., EPOM) in AS processes. Thus, the question arises whether it is really acetate or POM, which is important for the removal of phosphate in full‐scale AS plants. AS was harvested from a full‐scale anaerobic/aerobic AS plant. The amount of phosphate released after the addition of acetic acid depends on the AS conditions, particularly the influent sewage quality. However, the amount of phosphate released by EPOM was not affected by the AS conditions, and the amount of phosphate released per AS concentration and per unit of time was calculated to be about 0.86 mg PO₄‐P/g MLSS/hour. When the AS concentration is 2.5 g/L and the mixed‐liquor retention time is 2 hours in the anaerobic zone, about 4 mg/L PO₄‐P is released from EPOM. Under these conditions, phosphate in such sewage is removed by full‐scale AS plants without using acetic acid. In the case of carbon deficiency, the introduction of primary sludge to the anaerobic zone promoted the release of phosphate.     

Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

The goal of the study was to determine the effectiveness of nitrification and denitrification and the kinetics of ammonia removal from a mixture of wastewater and anaerobic sludge digester supernatant in an SBR at limited oxygen concentration. In addition, the COD removal efficiency and sludge production were assessed.In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O₂/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of K_m and V_max, calculated from the Michaelis-Menten equation, were 43 mg N-NH₄/L and 15.64 mg N-NH₄/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d⁻¹.     

The influence of anaerobic pretreatment on the nitrogen removal from biosynthetic pharmaceutical wastewaters

The C:N ratio of the pharmaceutical wastewaters is usually suitable for a combination of the anaerobic pretreatment with the high COD removal and aerobic posttreatment with the efficient biological N removal. This kind of anaerobic-aerobic process was tested in semipilot scale by using a UASB reactor and an activated sludge system with a predenitrification (total volume 100 1). It was found that at a total HRT of 2.3 days an average of 97.5% of COD and 73.5% of total N was removed. The UASB reactor was operated at 30°C with a volumetric loading rate of 8.7 kg.m^-3.d^-1, the efficiency of COD removal was 92.2%. The processes, which take part in the biological removal of nitrogen, especially the nitrification, were running with lower rates than usually observed in aerobic treatment systems.Abbreviations AAO anaerobic anoxic oxic configuration - AOO anaerobic oxic oxic configuration - B _V volumetric organic loading rate (kg COD.m^-3. d^-1) - dB _x specific COD removal rate (mg COD. g^-1 VSS. d^-1) - DNR denitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - E_COD efficiency of COD removal (%) - HRT hydraulic retention time (d) - NR nitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - R recirculation ratio (%) - SBP specific biogas production (m³.kg^-1 removed COD) - SRT solids retention time; sludge age (d) - SS suspended solids (g.1^-1) - UASB upflow anaerobic sludge blanket reactor - VSS volatile suspended solids (g.1^-1)     

Effects of an external magnetic field on the sedimentation of activated sludge

By applying an external magnetic field (800–3000 G, 0.08–0.30 T) using permanent magnets to the aeration vessel of an activated sludge culture, the sedimentation of activated sludge was enhanced and chemical oxygen demand (COD) removal was also improved in an indoor continuous culture system. Adding a small amount of iron(III) chloride (FeCl₃, less than 0.1%, w/v) stimulated these enhancements. The possibility was suggested that the small amount of molecular iron incorporated into the activated sludge stimulated the flocculation and sedimentation by external magnetization.     

Phosphorus removal by pure and mixed cultures of microorganisms

The ability to remove inorganic phosphate from synthetic wastewater was tested with about 40 microbial strains, and Pseudomonas aeruginosa IAM 1007 was found to give good performance under aerobic conditions. However, the phosphate removal under batch anaerobic/aerobic (A/O) treatment was not satisfactory in pure cultures of several strains including P. aerginosa, and Aceinetobacter calcoaceticus, but the activated sludge from a plant with an A/O process almost depleted the phosphate. Mixed cultures of P. aeruginosa in the presence of the facultativelu anaerobic strains of A-1 or A-8 isolated from the activated sludge showed enhanced phosphate removal. This suggests a symbiotic effect among microbial species on biological removal of inorganic phosphate in the A/O process.     

Fundamental Mechanisms of Phosphate Removal by Anaerobic/Aerobic Activated Sludge in Treating Municipal Wastewater

Acetate is thought to be an important substrate for phosphate removal in anaerobic/aerobic activated sludge (AS) processes. The acetate content in municipal wastewater is low, and the main organic compounds in such wastewater are particulate organic matters (POMs) that are converted to endogenous substrates in AS processes when municipal wastewater is introduced into AS reactors. The question which then arises is which substrate, acetate or POM, is important for phosphate removal in full‐scale AS plants. The rates of phosphate release and substrate uptake were determined using AS harvested from a full‐scale anaerobic/aerobic AS plant and also AS acclimated to peptone under alternate anaerobic and aerobic conditions for 26 months. The rate of phosphate release upon POM addition per AS concentration per unit of time was about 0.84 mg PO₄‐P/(g MLSS·h) irrespective of the wastewater quality. This value was about 0.05 in the case of AS acclimated to peptone for 26 months. When the AS concentration is 2.5 g/L and the mixed liquor retention time is 2 h in the anaerobic zone, about 4.2 mg/L PO₄‐P is released upon POM addition. Hence, phosphate can be removed from municipal wastewater using full‐scale AS plants running under these conditions.     

Evaluation of sludge reduction by an environmentally friendly chemical uncoupler in a pilot-scale anaerobic/anoxic/oxic process

An environmentally friendly chemical, tetrakis(hydroxymethyl)phosphonium sulfate (THPS), was used as a metabolic uncoupler to reduce sludge production in a pilot-scale anaerobic/anoxic/oxic process. The results show that the addition of THPS (1.08–1.86 mL/m³ influent) in the sludge return section could reduce waste activated sludge by about 22.5 %, and decrease the sludge yield by about 14.7 % at the end of a run. At the same time, the addition of THPS slightly lowered the removal of chemical oxygen demand (COD), soluble COD and NH₄ ⁺–N, and slightly improved removal of total nitrogen. The effects of THPS addition on two characteristics of activated sludge in oxic tank are discussed in detail and the results suggest that the settleability of sludge was reduced by addition of THPS, while the specific oxygen uptake rate was increased. Molecular biology analysis shows that the addition of THPS had little effect on the microbial communities of sludge.     

Verification of enhanced phosphate removal capability in pure cultures of<Emphasis Type="Italic">Acinetobacter calcoaceticus</Emphasis> under anaerobic/aerobic conditions in an SBR

Laboratory experiments were conducted using pure cultures ofAcinetobacter under anaerobic/aerobic cyclic conditions to explain the release and uptake of soluble phosphate in an activated sludge process showing enhanced biological phosphate removal (EBPR). Under anaerobic/aerobic cyclic conditions in a Sequencing Batch Reactor (SBR), COD uptake concurrent with soluble phosphate release byAcinetobacter was not significant during the anaerobic periods, indicating that EBPR would not be established in pure cultures. However,Acinetobacter cells accumulated higher phosphate content (5.2%) in SBR than that obtained (4.3%) from batch experiments. These results suggest thatAcinetobacter sp. may not follow the proposed pattern of behavior of poly-P bacteria in EBPR activated sludge plants.     

Effect of basic operating parameters on biological phosphorus removal in a continuous-flow anaerobic–anoxic activated sludge system

A continuous-flow anaerobic–anoxic (A2) activated sludge system was operated for efficient enhanced biological phosphorus removal (EBPR). Because of the system configuration with no aeration zones, phosphorus (P) uptake takes place solely under anoxic conditions with simultaneous denitrification. Basic operating conditions, namely biomass concentration, influent carbon to phosphorus ratio and anaerobic retention time were chosen as variables in order to assess their impact on the system performance. The experimental results indicated that maintenance of biomass concentration above 2,500 mg MLVSS/L resulted in the complete phosphate removal from the influent (i.e. 15 mg PO₄ ³⁻-P/L) for a mean hydraulic residence time (HRT) of 15 h. Additionally, by increasing the influent COD/P ratio from 10 to 20 g/g, the system P removal efficiency was improved although the experimental results indicated a possible enhancement of the competition between phosphorus accumulating organisms (PAOs) and other microbial populations without phosphorus uptake ability. Moreover, because of the use of acetate (i.e. easily biodegradable substrate) as the sole carbon source in the system feed, application of anaerobic retention times greater than 2 h resulted in no significant release of additional P in the anaerobic zone and no further amelioration of the system P removal efficiency. The application of anoxic P removal resulted in more than 50% reduction of the organic carbon necessitated for nitrogen and phosphorus removal when compared to a conventional EBPR system incorporating aerobic phosphorus removal.     

Anaerobic digestion of a petrochemical effluent using an anaerobic hybrid digester

Summary An anaerobic hybrid reactor was used in the anaerobic treatment of an acidic petrochemical effluent. An organic loading rate of 20.04 kg COD/(m³d) at a HRT of 17 hours was obtained with a volatile fatty acid removal of 91%, and COD removal of 84%. A final reactor effluent containing 44 mg/l ammonia nitrogen and 12.3 mg/l PO₄-P was produced.     

Anaerobic granule development for removal of pentachlorophenol in an upflow anaerobic sludge blanket (UASB) reactor

The granulation process using synthetic wastewater containing pentachlorophenol (PCP) in four 1.1 l laboratory scale upflow anaerobic sludge blanket (UASB) reactors was studied, and the anaerobic biotransformation of PCP during the granulation process investigated. After 110 days granular sludge was developed and up to 160 and 180 mg/l of PCP was added into the reactors R1 and R2, respectively, when they were inoculated with acclimated anaerobic sludge from an anaerobic digester of a citric acid plant. The inoculum was predominately composed of bacilli and filamentous bacteria. Granulation did not occur in reactors R3 and R4 which were inoculated with acclimated anaerobic sludge from aerobic sludge of the municipal sewage treatment plant which consisted mainly of cocci. Despite similar bacilli in the granule, the filamentous bacteria from reactor R1 were thicker than those of reactor R2. The granular sludge had a maximum diameter of 2.5 and 2.2 mm, and SMA of 1.44 and 1.32 gCOD/gTVS per day for reactors R1 and R2, respectively. Over 98% chemical oxygen demand (COD) removal rate and 99% of PCP removal rate were achieved when reactors R1 and R2 were operated at PCP and COD loading rates of 150 and 7.5 g/l per day, respectively. H₂-producing acetogens were the dominant anaerobes in the granular sludge.