Aeration of anaerobically digested sewage sludge for COD and nitrogen removal: optimization at large-scale.

The paper will report about the experiences at an Austrian large wastewater treatment plant of 720,000 population equivalents, where anaerobically digested sewage sludge is further stabilised under aerobic conditions. Enhanced stabilisation of the anaerobically digested sludge was required at the plant in order to get a permit for landfill disposal of the dewatered stabilized sludge. By implementing a post-aeration treatment (SRT approximately 6d; 36 degrees C) after anaerobic digestion the organic content of the anaerobically well digested sludge can be decreased by 16%. Investigations on site showed that during digested sludge post-aeration anoxic phases for denitrification are needed to provide stable process conditions. In this way the pH value can be kept in a more favourable range for micro-organisms and concrete structures. Additionally, inhibition of the biological process due to nitrite accumulation can be avoided. By optimising the aeration/pause ratio approximately 45% of total nitrogen in digested sludge can be removed. This significantly improves nitrogen removal efficiency at the wastewater treatment plant. NH(4)-removal occurs mainly through nitritation and denitritation with an efficiency of 98%. The costs/benefit analysis shows that post-aeration of digested sludge results in an increase of total annual costs for wastewater treatment of only 0.84%, corresponding to 0.19 Euro/pe/a. Result of molecular biological analyses (DGGE) indicate that all four ammonium-oxidizing bacteria species present in activated sludge can survive anaerobic digestion, but only two of them can adapt in the digested sludge post-aeration tanks. Additionally, in the post-aerated digested sludge a further ammonium-oxidizing bacteria species was identified.     

Biodegradability enhancement of municipal landfill leachate

The method of enhancing the biodegradability of landfill leachate via air stripping followed by coagulation/ultrafiltration （UF） processes is introduced. In this study, the air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen （NH3-N）, at an air-to-liquid ratio （A/L） of 3 300 （pH = 11） and after 18 h of stripping. The single coagulation process increased the BOD （biological oxygen demand）/COD （chemical oxygen demand） ratio by 0.089 with a FeCl3 dosage of 570 mg/L, at pH 7.0, and the single UF process increased the BOD/COD ratio from 0.049 to 0.311. However, the combination of coagulation and UF increased the BOD/COD ratio from 0.049 to 0.423, and the final BOD, COD, NH3-N, and colour of the leachate were 1 023 mg/L, 2 845 mg/L, 145 mg/L, and 2 056, respectively, when a 3 kDa molecular weight cut-off （MWCO） membrane was used at an operating pressure of 0.7 MPa. In the ultrafiltration process, the average solution flux （Jv）, concentration multiple （Mc）, and retention rate （R） for the COD were 107.3 L/（m^2·h）, 6.3, and 84.2%, respectively.     

Nitrogen removal from digested manure in a simple one-stage process

A process based on partial nitrification and recirculation into the anaerobic digester was studied to remove nitrogen from digested manure and thus reduce enhanced gaseous ammonia emissions due to on-farm biogas production. An anaerobic reactor representing an anaerobic manure digester was fed with a nitrite solution and digested manure liquor. Nitrite was efficiently removed from the influent and ammonium formation was observed first. Ammonium was subsequently eliminated up to a maximum of 90% of the influent concentration, indicating anaerobic ammonium oxidation activity. This activity, however, decreased again and was lost at the end of the 4-month operation period. In a 1.5 L aerobic CSTR that was fed with digested manure liquor, ammonium was efficiently removed from the influent. Nitrite and nitrate formation was observed but mass balances indicated significant N-removal. Accumulation of suspended solids was observed at the end of the experiment suggesting presence of oxygen-free environments. In a second test in a 15 L CSTR where suspended solids sedimentation could be avoided, low N-removal rates were observed in the absence of biofilm carrier elements whereas high N-removal rates were achieved in their presence. A simple one-stage process based on immobilized biomass could therefore be installed downstream of agricultural anaerobic digesters in order to mitigate undesirable gaseous ammonia emissions.     

Post-aeration of anaerobically digested sewage sludge for advanced COD and nitrogen removal: results and cost-benefit analysis at large-scale.

At a large Austrian municipal wastewater treatment plant enhanced stabilisation of anaerobically digested sewage sludge was required in order to get a permit for landfill disposal of the dewatered stabilized sludge. By implementing a post-aeration treatment after anaerobic digestion the organic content of the anaerobically well digested sludge can be decreased by 16%. Investigations at this plant showed that during digested sludge post-aeration anoxic phases are needed to provide stable process conditions. In this way the pH value can be kept in a more favourable range for micro-organisms and concrete structures. Additionally, under the process conditions applied nitrite accumulation would inhibit the stabilisation process if denitrification is not adequately applied. By optimising the aeration/pause ratio approximately 45% of total nitrogen in digested sludge can be removed. NH4-removal occurs through nitrification and denitrification with an efficiency of 98%. This significantly improves nitrogen removal efficiency at the wastewater treatment plant. The costs/benefit analysis shows that post-aeration of digested sludge results in an increase of total annual costs for wastewater treatment of only 0.84%, corresponding to 0.19 Euro/pe/a. Specific costs for nitrogen removal (0.32 Euro/kgN) are comparable with other biological processes for N-removal in reject water.     

Application of PTFE membrane for ammonia removal in a membrane contactor

The feasibility of a membrane contactor system for ammonia removal was studied. The mass transfer coefficient was used to quantitatively compare the effect of various operation conditions on ammonia removal efficiency. Effective removal of ammonia was possible with a Polytetrafluoroethylene (PTFE) membrane contactor system at all tested conditions. Among the various operation parameters, contact time and solution pH showed significant effect on the ammonia removal mechanism. The overall ammonia removal rate was not affected by influent suspended solution concentration unlike other pressure driven membrane filtration processes. Also the osmotic distillation phenomena which deteriorate the mass transfer efficiency can be minimized by preheating of influent wastewater. A membrane contactor system can be a possible alternative to treat high strength nitrogen wastewater by optimizing operation conditions such as stripping solution flow rate, influent wastewater temperature, and influent pH.     

Anaerobic digestion of slaughterhouse waste with UF-membrane separation and recycling of permeate after free ammonia stripping.

Anaerobic digestion can adapt to free ammonia to a certain extent. During the anaerobic digestion of slaughterhouse waste, however, an ammonia concentration of up to 15 g Nl(-1) can be reached in the sludge liquid and this will even inhibit adapted sludge. To lower this concentration, a fraction of the digester liquid must therefore be continuously separated from the digested sludge and the free ammonia stripped before the liquid is recycled to the digester. A mesophilic laboratory digester was successfully operated with an ammonium concentration of 4-5g l(-1) and a pH of 8.0-8.4. After free ammonia stripping, the excess liquid was treated in a laboratory SBR for nitrogen and phosphorus removal before being added to the receiving water. The effluent had no toxic effect on daphnia and algae.     

Aeration effect on the efficiency of swine manure treatment in a trickling filter packed with organic materials.

Effect of aeration rate on the removal of organic matter and nitrogen and on the formation of NH3, N2O and N2 was studied for an extensive biofiltration system packed with an organic media, which was used to treat pig manure. The results show high removal of BOD5 and TSS (99 and > or = 98%), independently of the four aeration rate tested (3.4-34 m3/m2 x h). Aeration rate > or = 4.4 m/h resulted in high ammonia stripping during start-up (> or = 1.0 kg NH3-N/m3 of swine manure treated), while using 3.4 m/h only 0.3 kg NH3-N/m3 were stripped. Complete nitrification was achieved after day 100 of operation, except in the biofilter with the lowest aeration rate. Simultaneous denitrification established in all the biofilters. Applying an aeration rate of 9.4 m/h up to 1.2 kg nitrogen was removed in the form of N2 for each m3 of swine manure treated. Contrary to the expectations, N2 formation and release increased with the aeration rate. This particular behaviour seems to be related to the punctual accumulation of water layers inside the biofilters, caused by the air force flowing in the opposite direction to the water flux. N2O production was quite similar in all biofilters (between 0.25-0.36 kg N2O-N/m3 of swine manure treated).     

Treatment of anaerobically digested dairy manure in a two-stage biofiltration system

High concentrations of ammonium and phosphate present a challenge to cost-effective treatment of anaerobically digested dairy manure. This study investigated the efficacy of a two-stage biofiltration system for passive treatment of digested dairy manure. The first stage pebble filters were batch loaded. When the slurry-like digested dairy manure was retained on pebble beds, soluble contaminants were removed before liquid infiltrated over 8-17 days. The pebble filters removed 70% of soluble chemical oxygen demand, 71% of soluble biochemical oxygen demand, 75% of ammonium, and 68% of orthophosphate. Nitrogen removal was attributed to the conventional nitrification - denitrification process and novel nitritation - anammox process. Aerobic ammonium oxidizing and anammox bacteria accounted for 25 and 23% of all bacteria, respectively, in the filtrate of the pebble filters. The longer it took for filtration, the greater the removal efficiency of soluble contaminants. The second stage sand filters had removal efficiencies of 17% for soluble chemical oxygen demand, 45% for soluble biochemical oxygen demand, 43% for ammonium, and 16% for orthophosphate during batch operations at a hydraulic retention time of 7 days. Aerobic ammonium oxidation and anammox were primarily responsible for nitrogen removal in the sand filters. Vegetation made an insignificant difference in treatment performance of the sand filters.     

Possible use of feed water for boiler injectors

The operation of steam desuperheaters with injector devices with water supply from condensate equipment in boiler units is analyzed. An analysis is given of articles which demonstrate the feasibility of transferring the regulation of the steam temperature in desuperheaters by the condensate itself to regulation by injection of feed water. Schemes are proposed for supply of feed water with the possibility of using a regulator valve. Schemes involving the installation of hardware in the feed line that ensures the required leak tightness, pressure drop, throttling and flow rate, are examined, and a scheme is proposed for modernization of startup injection. Translated from élektricheskie Stantsii, No. 8, August 2008, pp. 17–24.     

The dissolution characteristics of calcium sulfide and utilization as a precipitation agent in acidic wastewater effluent treatment

The dissolution characteristics of CaS in the presence of CO2 has been investigated by monitoring sulfide speciation, solution conductivity and pH during dissolution. The sulfide speciation associated with CaS dissolution was utilized for metal precipitation from acidic wastewater effluents. The mechanism involved in the dissolution process was observed to be pH-dependent, characterized by increased solution conductivity as the HS(-) species becomes dominant in solution in the form of the Ca(HS)2 complex. The replacement of HS(-) by CO3(2-) in the Ca(HS)2 complex triggered CaCO3 precipitation and H2S stripping and this was characterized by decreased solution pH and conductivity. The sulfide to total metal molar ratio was observed to have an effect on the pH and therefore sulfide speciation as well as extent of metal removal. The utilization of CaS in the treatment of acidic wastewater effluents demonstrated complete metal removal, with the potential of a pH-controlled selective metal removal and recovery.     

Odour abatement in the integrated reactor concept for simultaneous treatment of liquid and solid pig manure fractions.

New technologies are needed for manure treatment that can capture nutrients, reduce emissions of ammonia and nuisance odours, and kill harmful pathogens. A reactor concept was developed for simultaneous treatment of separately collected liquid and solid fractions of pig manure. The liquid fraction is concentrated by evaporating the water using energy from the composting system and at the same time scrubbing ammonia from the composting off-gas by acidifying the urine to pH 4 with nitric acid. This results in two marketable products, a concentrated liquid nitrogen fertiliser (NH4NO3) without phosphorus, and a stabilised, solid organic fertiliser, which is free of pathogens and weeds. By connecting the two reactor systems, emissions of ammonia and odours are abated as ammonia emitted from the composting is trapped in the liquid fraction and odorous compounds emitted from the liquid are degraded in the composting reactor. The concept was physically simulated by coupling a 80-L compost reactor to a 10-L bubble column. Operation of the bench-scale system showed that the concept is very promising. All nutrients were captured, and emissions of ammonia and odours were almost completely abated.     

Integrated biological (anaerobic-aerobic) and physico-chemical treatment of baker's yeast wastewater.

The UASB reactor (35 degrees C) was quite efficient for removal of bulk COD (52-74%) from simulated (on the basis of cultivation medium from the first separation process) general effluent of baker's yeast production (the average organic loading rates varied from 8.1 to 16 g COD/l/d). The aerobic-anoxic biofilter (19-23 degrees C) can be used for removal of remaining BOD and ammonia from anaerobic effluents; however, it suffered from COD-deficiency to fulfil denitrification requirements. To balance COD/N ratio, some bypass (approximately 10%) of anaerobically untreated general effluent should be added to the biofilter feed. The application of iron (III)-, aluminium- or calcium-induced coagulation for post-treatment of aerobic-anoxic effluents can fulfil the limits for discharge to sewerage (even for colour mainly exerted by hardly biodegradable melanoidins), however, the required amounts of coagulants were relatively high.     

Application of biofilm reactors to improve ammonia oxidation in low nitrogen loaded wastewater

An airlift reactor using zeolite particles as carrier material was used for the nitrification of effluents from the aquaculture industry. During the start-up the nitrogen concentration was kept around 100 mg NH4(+)-N/L to develop the nitrifying population. Later it was decreased down to around 3 mg NH4(+)-N/L and the dilution rate was increased up to 4.8 d(-1) in order to simulate the conditions in a an aquaculture waster treatment system. A nitrogen loading rate (NLR) of 535 mg NH(+)-N/m2 d was fully oxidized to nitrate. Higher values of NLRs caused nitrite accumulation. A second biofilm reactor was fed with a synthetic medium containing 50 mg NH4(+)-N/L which simulated the effluents from anaerobic units treating domestic wastewater. A nitrogen loading rate of 400 mg NH4(+)-N/L d was oxidized into nitrate with an efficiency of 60% at a dilution rate of 8 d(-1). Both biofilm systems allowed the development of a nitrifying population to treat the studied types of wastewaters.     

Anaerobic monodigestion of poultry manure: determination of operational parameters for CSTR

In this work the anaerobic monodigestion for the treatment of turkey manure was evaluated, without its codigestion with another substrate. The effect of the organic loading rate (OLR) and the substrate concentration (high total solids (TS) concentration) or product concentration (high volatile fatty acids (VFA) and/or ammonia (NH(3)-N) concentrations) was studied. The results show that for a continuous stirred tank reactor (CSTR) operation, a maximum of 40 g/L of TS and 4.0 g/L of ammonium (NH(4)(+)) was required. In addition, the maximum organic loading rate (OLR) will not exceed 1.5 kg VS/m(3)d. Higher TS and NH(4)(+) concentrations and OLR lead to a reduction on the methane productivity and volatile solids (VS) removal. During the CSTR operation, a high alkalinity concentration (above 10 g/L CaCO(3)) was found; this situation allowed maintaining a constant and appropriate pH (close to 7.8), despite the VFA accumulation. In this sense, the alkalinity ratio (α) is a more appropriate control and monitoring parameter of the reactor operation compared to pH. Additionally, with this parameter a VS removal of 80% with a methane productivity of 0.50 m(3)(CH4)/m(3)(R)d is achieved.     

Enhanced heavy metals removal without phosphorus loss from anaerobically digested sewage sludge

Heavy metals removal without phosphorus loss from anaerobically digested sewage sludge was investigated by conducting batch experiments using hydrogen peroxide and/or iron sulphate under acidified conditions at pH 3. The addition of hydrogen peroxide to the sludge improved the elution efficiencies of As, Cd, Cu and Zn with phosphorus loss from the sludge. The optimum initial concentrations of hydrogen peroxide were. Respectively. 0.1% for As, Cd, Mn and Zn and 0.5% for Cu and Ni. The combined process of 0.1% hydrogen peroxide and 1 g Fe/L ferric sulphate enhanced the initial elution rate of Cu and Cr compared to the addition of either ferric sulphate or hydrogen peroxide, indicating that oxidants stronger than hydrogen peroxide were produced in the sludge. Furthermore, the combined process immobilised phosphorus in the sludge due to co-precipitation with ferric hydroxide or precipitation as ferric phosphate. It was concluded that there is a possibility that the combined process could remove heavy metals effectively without phosphorus loss from anaerobically digested sewage sludge.     

天津市于桥水库水质变化特点及影响因素分析

采用非参数Mann-Kendall检验和Sen方法对于桥水库1986-2005年的水质参数(pH值、DO,COD,BOD5和NH3-N)的变化趋势和趋势量进行了统计和分析.结果表明:近20年来于桥水库水质能够满足其水功能规划Ⅲ类水质标准要求,pH值、D0,BOD5和NH3-N质量浓度均达到Ⅱ类水质标准,COD质量浓度也...     

Full-scale applications for both COD and nutrient removal in a CIRCOX airlift reactor.

The airlift reactor technology has been successfully applied at full scale for both COD and nitrogen removal. In this study, the results of the biofilm development and biological performance of two full scale reactors are discussed. At Paulaner Brewery in Munich, the airlift reactor was applied for COD and ammonia removal of anaerobically treated wastewater. In the other case the airlift reactor was applied as a pretreatment of nitrogen removal by the Anammox process. Water from a Tannery company in Lichtenvoorde in the Netherlands, The Hulshof Royal Dutch Tanneries, was pretreated anaerobically for COD removal and aerobically to remove the sulphides as sulphur. In an airlift reactor the ammonia was partially oxidised to nitrite. In both cases the granular biomass developed well; the concentrations amounted to 250 microl/L and 500 ml/L respectively. In the first case, 4 kg/m(3)/day of COD was removed, the soluble concentration of COD was less than 250 mg/L. The nitrification to nitrate was nearly complete and amounted to 0.5 kg NH4-N/m(3)/day. In the second application, 50% of the ammonia (on average 0.45 kg N/m3/d) was nitrified to nitrite. This process was easily controlled by regulating the amount of air according to the nitrite and ammonia concentrations in the effluent. It can be concluded that in both cases the particular processes were very stable and easy to operate.     

Ammonia oxidizing bacterial community composition and process performance in wastewater treatment plants under low temperature conditions

Nitrification can be difficult to maintain at wastewater treatment plants (WWTPs) during cold periods resulting in disrupted nitrogen removal. The aim of this study was to relate nitrification process performance to abundance and composition of the ammonia oxidizer communities in two closely located municipal WWTPs in Sweden during an eight month period covering seasonal changes and low temperature conditions. Both facilities showed lower NH(4)(+)-N removal efficiency and nitrification rates as temperature decreased. However, one of the plants had a more stable nitrification rate and higher ammonia removal efficiency throughout the entire period. The differences in performance was related to a shift in the composition of the bacterial ammonia oxidizing community from a Nitrosomonas oligotropha-dominated community to a mixed community including also Nitrosomonas ureae-like ammonia oxidizers. This was likely a response to differences in NH(4)(+)-N and organic loading.     

The role of iron and aluminium in digestion and odor formation.

The role of iron and aluminium in determining volatile solids reduction and odors from anaerobically digested, dewatered sludge cakes was evaluated from data collected from a variety of wastewater treatment plants. It was found that volatile solids reduction generally increased as the iron content of the sludge increased. It was also observed that odors increased with increasing iron. No correlation with aluminium or divalent cations was found. Based on these data it appears that the volatile solids reduction by anaerobic digestion is not useful for predicting the odors from anaerobically digested sludges.     

Online headspace chromatographic method for measuring VFA in biogas reactor.

A headspace chromatographic method has been applied to measure volatile fatty acids in anaerobic digesters using gas phase extraction at pH less than 2 and temperature higher than 65 degrees C. The concentration of volatile fatty acids in liquid and gas phase can be correlated in the form of Henry's coefficient. Analysis of different factors in the batch indicated that pH, temperature, and salt addition had a strong impact on apparent solubility, while liquid/gas volume ratio and organic acid concentration had little impact. Larger liquid volume had a positive impact on extraction efficiency, while increased gas headspace had a negative impact, indicating that the system was total mass-limited. The best conditions were at pH < 2.0, and temperatures above 75 degrees C. The advantage of an automated gas-extraction system for organic acid analysis, compared to an automated liquid system is that it contains no filter element, which is 4 susceptible to fouling in manure samples or samples with high solid content. An automated system which included a valerate pulse to the parent reactor was implemented, and operated for a short period.