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This study investigates the potential of hydrodynamically disintegrated excess activated sludge when used as a supplementary carbon source for denitrification. Two objectives constituted this study: (i) to analyse the denitrification rate by using excess sludge subjected to hydrodynamic disintegration (HD), performed at different energy densities, as an organic carbon source, and (ii) to analyse the impact of hydrolysis of disintegrated sludge on the denitrification rate. Nitrate reduction tests were conducted to assess the denitrification rate for the following sources of organic carbon: thickened excess sludge disintegrated at three levels of energy density (70, 140 and 210 kJ/L), acetic acid solution and municipal wastewater after mechanical treatment. It was found that the HD of excess sludge conducted at different levels of energy density led to dissolved organic compounds characterised by various properties as donors of H+ in the denitrification process. The susceptibility of disintegrated sludge to anaerobic hydrolysis decreased along with the increasing energy density. The obtained organic carbon contributed to a lower increase in the denitrification rate in comparison to that when disintegrated sludge not subjected to hydrolysis was applied. [ABSTRACT FROM AUTHOR]

The goal of the study was to evaluate the possibility of carbon source recovery from excess sludge by mechanical disintegration for biological denitrification. The total efficiency of denitrification, unit demand for organic compounds for denitrification, unit volume of disintegrated sludge and unit cost of nitrogen removal as a function of energy density used for excess sludge disintegration (70, 140 and 210 kJ/L) were analyzed. In the study a full-scale disc disintegrator was used (motor power: 30 kWh, motor speed: 2,950 rpm). It was shown that the amounts of organic compounds released from the activated sludge flocs at all tested levels of energy density are high enough to be used to intensify the removal of nitrogen compounds from wastewater. It was also documented that the energy density provided during process of disintegration was an important factor determining the characteristics of organic compounds obtained under the disintegration for their use in order to intensify the process of denitrification. The highest value of total efficiency of denitrification (50.5± 3.1 mg N/L) was obtained for carbon source recovery from excess sludge at 70 kJ/L, but the lowest unit cost of nitrogen removal occurred for 140 kJ/L (0.0019± 0.0011 EUR/g N). [ABSTRACT FROM AUTHOR]

To investigate the feasibility of using corncob charcoal substrate in constructed wetlands, four laboratory-scale vertical flow constructed wetlands (VFCWs) were built. Effluent pollutant (chemical oxygen demand (COD), NH4+-N, total phosphorus (TP)) concentrations during the experiment were determined to reveal pollutant removal mechanisms and efficiencies at different stages. In the stable stage, a VFCW using clay ceramisite substrate under aeration attained higher COD (95.1%), and NH4+-N (95.1%) removal efficiencies than a VFCW using corncob charcoal substrate (91.5% COD, 91.3% NH4+-N) under aeration, but lower TP removal efficiency (clay ceramisite 32.0% and corncob charcoal 40.0%). The VFCW with raw corncob substrate showed stronger COD emissions (maximum concentration 3,108 mg/L) than the corncob charcoal substrate (COD was lower than influent). The VFCW using corncob charcoal substrate performed much better than the VFCW using clay ceramisite substrate under aeration when the C/N ratio was low (C/N = 1.5, TN removal efficiency 36.89%, 4.1% respectively). These results suggest that corncob charcoal is a potential substrate in VFCWs under aeration with a unique self --supplying carbon source property in the denitrification process. Key words | aeration, C/N ratio, carbon source, charcoal, constructed wetlands, denitrification [ABSTRACT FROM AUTHOR]

The aim of the present work was to evaluate the effects of carbon sources and chemical oxygen demand (COD)/NO2 --N ratios on the anammox-denitrification coupling process of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm. Also, the anammox activities of the SNAD biofilm were investigated under different temperature. Kaldnes rings taken from the SNAD biofilm reactor were operated in batch tests to determine the nitrogen removal rates. As a result, with the carbon source of sodium acetate, the appropriate COD/NO2 --N ratios for the anammox-denitrification coupling process were 1 and 2. With the COD/NO2 --N ratios of 1, 2, 3, 4 and 5, the corresponding NO2--N consumption via anammox was 87.1%, 52.2%, 29.3%, 23.7% and 16.3%, respectively. However, with the carbon source of sodium propionate and glucose, the anammox bacteria was found to perform higher nitrite competitive ability than denitrifiers at the COD/NO2--N ratio of 5. Also, the SNAD biofilm could perform anammox activity at 15 WC with the nitrogen removal rate of 0.071 kg total inorganic nitrogen per kg volatile suspended solids per day. These results indicated that the SNAD biofilm process might be feasible for the treatment of municipal wastewater at normal temperature. [ABSTRACT FROM AUTHOR]

A sequencing batch reactor was used to investigate the effect of carbon sources on the metabolism of activated sludge. Acetate and phenol, with the chemical oxygen demand (COD) of 330-350 mg L-1, was used as the carbon source in Periods I and II, respectively. Acetate decreased in the initial 120 min with the intracellular storage materials (XSTO), extracellular polymeric substances (EPS), and the soluble microbial products (SMP) accumulating to 131.0 mg L-1, 347.5 mg L-1, and 35.5 mg L-1, respectively. Then, XSTO and EPS decreased to 124.5 mg L-1 and 340.0 mg L-1, respectively, in the following 120 min. When acetate was replaced by phenol, it could not be used at the beginning due to its toxicity. The XSTO decreased from 142 mg L-1 to 54.6 mg L-1 during the aeration period. The EPS had a significant increase, with the highest value of 618.1 mg L-1, which then decreased to 245.6 mg L-1 at 240 min. The phenol was gradually degraded with the acclimation and it can be fully degraded 18 d later. Meanwhile, the usage ratio of the internal carbon source decreased. The effluent SMP in Period II was 1.7 times that in Period I. [ABSTRACT FROM AUTHOR]

An acidification metabolite such as volatile fatty acids (VFAs) and ethanol could be used as denitrification carbon sources for solving the difficult problem of carbon source shortages and low nitrogen removal efficiency. A proper control of environmental factors could be essential for obtaining the optimal contents of VFAs and ethanol. In this study, suspended solids (SS), oxidation reduction potential (ORP) and shaking rate were chosen to investigate the interactive effects on VFAs and ethanol production with waste sludge. It was indicated that T-VFA yield could be enhanced at lower ORP and shaking rate. Changing the SS, ORP and shaking rate could influence the distribution of acetic, propionic, butyric, valeric acids and ethanol. The optimal conditions for VFAs and ethanol production used as a denitrification carbon source were predicted by analyzing response surface methodology (RSM). [ABSTRACT FROM AUTHOR]

In this study, by-products from alcohol productionwere examined in terms of their potential application as external carbon sources for enhancing denitrification in biological nutrient removal systems. Three types of batch tests were used to compare the effects of the distillery by-products, such as fusel oil, syrup and reject water, on the non-acclimated activated sludge. Much higher nitrate utilization rates (NURs) were observed for the latter two carbon sources. In the conventional NUR measurements (onephase experiments), the observed NURs with syrup and reject water were 3.2-3.3 g N/(kg VSS h) compared with 1.0 g N/(kg VSS h) obtained for fusel oils fromtwo different distilleries. When the carbon sources were added at the beginning of the anoxic phase preceded by an anaerobic phase (two-phase experiments), the NURs were 4.2 g N/(kg VSS h) (syrup and reject water) and 2.4-2.7 g N/(kg VSS h) (fusel oils). The heterotrophic yield coefficient, determined based on the conventional OUR measurements, varied in a relatively narrowrange (0.72-0.79 g COD/g COD) for all the examined carbon sources. Due to advantageous composition (much higher COD concentrations and COD/N ratios), fusel is a preferred carbon source for practical handling in full-scale wastewater treatment plants. [ABSTRACT FROM AUTHOR]

In this research the agricultural by-product corncob was investigated as a carbon source as well as a biofilm carrier to remove organic matter, expressed as chemical oxygen demand (COD) and nitrate nitrogen (nitrate-N), from wastewater in a batch laboratory reactor. The performance of a reactor with corncob as the carbon source and the biofilm carrier was compared with a control batch reactor with suspended plastic carriers and glucose as the sole carbon source. With 60 vol% of corncob carriers inside the reactor, a soluble COD/N ratio of 4.2 g COD g N-1 was enough for total denitrification, nearly half of the control reactor (9.5 g COD g N-11), at 23 h reaction time. The specific denitrification rate decreased with increasing soluble COD consumption for both reactors. Nitrate and COD removal efficiencies decreased with shorter retention times, with accentuated effects in the reactor. This study suggested corncob as a feasible carbon source and that reaction time was a limiting factor with corncob used as the carbon source for denitrification. [ABSTRACT FROM AUTHOR]

Biological nutrient removal requires sufficient carbon source. Meanwhile, the removal of organic matter in wastewater requires energy consumption in the aeration tank. Carbon source for nutrient removal in most wastewater treatment plants with conventional primary clarifier (CPC) is generally insufficient in China. In order to increase carbon source and to save energy, a part of the CPC may be retrofitted as an activated primary clarifier (APC). In this paper, a pilot scale experiment was conducted to examine the performance of primary sludge fermentation and its effect on nitrogen and phosphorus removal. Results show that the primary sludge fermentation in APC has produced a similar VFA/TP ratio but a higher BOD5/TN ratio compared with those in the CPC effluent, and the TN concentrations in the secondary effluent are at 8.0, 10.8, and 17.4 mg/L, while TP is at 0.45, 1.10, and 2.28 mg/L when the pilot test system was fed with (1) the APC effluent, (2) 50% from the APC effluent and 50% from the CPC effluent, and (3) the CPC effluent, respectively. Results also indicate that the BOD5/TN ratio is a more sensitive factor than the VFA/TP ratio for nutrient removal and energy conservation for the APC fermentation. [ABSTRACT FROM AUTHOR]

The paper describes an evaluation carried out on demonstration scale to show that it was possible to use a Hybrid Reed Bed System comprising a Horizontal flow and a Vertical Flow Bed for treating the high strength run-off from a fertiliser packaging plant. The site is located close to an estuary which is sensitive to nutrients. The environmental regulators were therefore concerned that excessive mass flows of nitrate, ammoniacal nitrogen and phosphate, potentially arising from the site run-off, were not discharged into the estuary. The fertiliser manufacturing company required a simple, low maintenance system for removing nitrogen and phosphorus. A series of experimental runs were carried out to characterise the performance of the Hybrid System, establishing the effluent quality that could be achieved and the mass removal rate which was appropriate for acceptable treatment. These tests showed that it was possible to achieve a reduction of 79% in Total N whilst using molasses as a carbon source for denitrification. When using a 4:1 recycle ratio this produced an effluent with concentrations of 14mgNH4-N/litre and 18mgNO3-N/litre from treating site run-off containing concentrations in the order of 75 mg/litre of both NH3N and NO3-N. Chemical dosing with an iron salt brought the P concentration down to around 0.5mgPO4-P/litre. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the feasibility of the re-use of the winery wastewater to enhance the biological nutrient removal (BNR) process. In batch experiments it was observed that the addition of winery wastewater mainly enhanced the nitrogen removal process because of the high denitrification potential (DNP), of about 130 mg N/g COD, of the contained substrates. This value is very similar to that obtained by using pure organic substrates such as acetate. The addition of winery wastewater did not significantly affect either phosphorus or COD removal processes. Based on the experimental results obtained, the optimum dosage to remove each mg of N-NO3 was determined, being a value of 6.7 mg COD/mg N-NO3. Because of the good properties of the winery wastewater to enhance the nitrogen removal, the viability of its continuous addition in an activated sludge pilot-scale plant for BNR was studied. Dosing the winery wastewater to the pilot plant a significant increase in the nitrogen removal was detected, from 58 to 75%. The COD removal was slightly increased, from 89 to 95%, and the phosphorus removal remained constant. [ABSTRACT FROM AUTHOR]

An application of hydrothermal reaction was investigated to reuse excess sludge as carbon sources for enhancement of biological phosphorus removal. Under the tested conditions, solubilization of treated excess sludge did not present much variation, sustaining around 65%, except the results obtained at 400 °C. Biodegradability of excess sludge was improved through its content change by the reaction, without much reduction of carbon contents even in 7min. From the results of respirometric test, readily biodegradable substrate was found at 300 °C. Then its portion of reaction products increased with increasing reaction temperature. In the readily biodegradable substrate, acetic and propionic acid, which are useful carbon sources for phosphorus accumulating microorganism under anaerobic condition, increased with increasing reaction temperature. Hydrothermal reaction might be accepted as suitable pretreatment method to treat excess sludge prior to biological treatment process. This technology also secures excess sludge reuse, enhancing biological phosphorus removal and improvement of biological treatment process. [ABSTRACT FROM AUTHOR]

The effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by denitrifying phosphorus removal bacteria sludge was systematically studied using batch experiments, at the same time the variation of ORP was investigated. Results showed that the denitrifying and phosphorus uptake rate in the anoxic phase increased with the high initial anaerobic carbon source addition. However, once the initial COD concentration reached a certain level, which was in excess of the PHB saturation of Poly-p bacteria, residual COD carried over to the anoxic phase inhibited the subsequent denitrifying phosphorus uptake. This was equal to supplementing the external carbon source to the anoxic phase, furthermore the higher the external carbon source concentration the more powerful the inhibition caused. High nitrate concentration in the anoxic phase increased the initial denitrifying phosphorus rate. Once the nitrate was exhausted, phosphate uptake changed to phosphate release. Moreover, the time of this turning point occurred later with the higher nitrate addition. On the other hand, through on-line monitoring the variation of the ORP with different initial COD concentration, it was found that ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the dinitrification and anoxic phosphorus uptake operations. [ABSTRACT FROM AUTHOR]

The effect of different carbon sources (propionate, acetate, butyrate and glucose) on an enhanced biological phosphorus removal biomass developed with propionate as the sole carbon source was studied. Firstly, a group of different cycle studies was carried out using each substrate independently and then, another cycle study was performed with a mixture of substrates. Propionate was found to be the substrate with the highest substrate uptake rate in both sets of experiments. It was also the volatile fatty acid (VFA) which required less reducing power and less P-release to be uptaken. Four different polyhydroxyalkanoate (PHA) monomers produced during the anaerobic phase were detected, and PHB, PHV and PH2MV were quantified. Significant differences in PHA composition were obtained depending on the carbon source. The carbon recovery ratio for the anaerobic phase was also evaluated. The lowest value observed among the different cycle studies was obtained for butyrate, while the highest value was obtained for acetate. [ABSTRACT FROM AUTHOR]

Anaerobic methanogenic consortia have a considerable resistance to oxygen exposure. Yet, most research has been focused on the study of the tolerance to oxygen of anaerobic immobilized biomass. Less is known on the potential of the anaerobic suspended biomass for withstanding exposure to oxygen and the effect of a primary degradable substrate on such resistance. Thus, the objective of this work was to determine the effect of the amount of a primary degradable substrate (sucrose) on the resistance of a methanogenic suspended biomass to oxygen exposure. It was found that the inhibition of disperse anaerobic sludge by oxygen exposure decreases when the concentration of the supplemented carbon source increases. This is in agreement with the fact that aerobic respiration of the added substrate by the facultative heterotrophic bacteria, always present in this type of sludge, has been found in previous studies as one of the main mechanisms protecting methanogens against O2. From a practical point of view, this suggests that aeration of anaerobic systems should be possible without inhibiting the activity of methanogenic bacteria if an adequate ratio between oxygen and COD feeding is maintained. Such a ratio will depend however on the wastewater initial COD concentration. [ABSTRACT FROM AUTHOR]

Ethanol and methanol were compared for their performance as carbon sources for denitrification. The study was carried out in two chemostats, operated in parallel on synthetic media containing ethanol and methanol respectively as carbon sources. In addition, pure culture studies were performed on one ethanol- and one methanol-utilizing denitrifier. Ethanol was found to be considerably more readily available as a carbon source for denitrification than was methanol. An efficient denitrification with ethanol was established in a short time, while denitrification with methanol required a substantial adaptation time and never showed the same stability as denitrification with ethanol. The growth rate of denitrifiers with ethanol as carbon source was 2-3 times higher than with methanol. The amount of COD required to denitrify a certain amount of nitrate was somewhat lower for ethanol (3.85 g/gN) than for methanol (4.45 g/gN) in the continuous experiments, while it was considerably higher for ethanol (6.1 g/gN) than for methanol (4.1 g/gN) th pure culture batch cultivations. [ABSTRACT FROM AUTHOR]

A method of determining the actual and potential denitrification rates in activated sludge samples by measuring accumulation of nitrous oxide after inhibition by acetylene was adapted and applied. Rates obtained with the acetylene inhibition technique were compared with those calculated through mass balances of total nitrogen from process data as well as those measured as nitrate utilisation. The acetylene inhibition technique was a reliable method for determination of denitrifying activity. The influence of acetate, ethanol, methanol and nitrate additions was examined. Acetate gave the best response upon denitrification followed by ethanol and methanol. The bacteria in the activated sludge could not denitrify at full capacity due to limitations in the supply of electron donors. The actual rates measured with the acetylene inhibition technique corresponded to the rates obtained from process data. The potential rates, determined with additions of acetate and nitrate in excess (240 mg 1-1 and 28 mg N 1-1), were 3-7 times higher than the actual rates and the rates calculated from process data. There is, thus, a potential for a more rapid denitrification rate. The potential denitrification rate measured with the acetylene inhibition technique was equivalent to the nitrate utilisation rate. [ABSTRACT FROM AUTHOR]

The possibility of using biologically hydrolysed sludge as carbon source for the denitrification process in biofilms has been investigated. The goal of the biological sludge hydrolysis process is a high degree of solubilization of the organic matter in the sludge. The soluble organic matter is best dominated by readily biodegradable compounds. The biological hydrolysis of chemical/biological raw sludge resulted in a degree of solubilization (yield) of 11%, where about 84% of the soluble organic matter originated from protein materials. The solubililized nitrogen was found as ammonium-nitrogen. The sludge was composed of 70% chemical sludge and 30% biological sludge. On average 66% of the soluble organic matter was volatile fatty acids. Only the volatile fatty acids were utilized as carbon source in the denitrifying biofilm. The biofilms were around 1000 µm thick, and the denitrification rate with respect to the concentration of volatile fatty acids could be described by a hyperbolic Monod-type function. The effect of the diffusion resistance in the biofilms was reflected by the use of an artificial "half-saturation" constant, K*CODVFA = 3 mg CODVFA/l. The maximum denitrification rate was found to be rNO-N3max = 0.57 g NO3-N/g VS· d. The stoichiometric consumption ratio between soluble organic matter and nitrate was 4.5 g CODVFA/g NO3-N on average. A simulation example on the nitrogen removal capacity when the carbon source is provided by sludge hydrolysis is given. [ABSTRACT FROM AUTHOR]

This paper is a contribution to the understanding of the possibilities and limitations of the socalled HYPRO-concept, a compact process design for nutrient removal where the carbon source for the denitrification process is provided by hydrolysis of the pre-precipitated sludge. The objective of the study was to investigate how efficiently biologically hydrolysed sludge is utilized in a biofilm process. The results show that only the volatile fatty acids in the hydrolysed sludge were utilized as carbon source. The denitrification kinetics were not influenced by the particulate and colloidal materials that adsorbed to the biofilm. The biofilms in the present study were thick (> 900 µn) and porous, and the denitrification rate could be described by a hyperbolic Monod-type function with respect to both the nitrate and the volatile fatty acids concentration. The diffusion resistance is included and expressed by an artificial "half-saturation" constant, K*. The maximum denitrification rate was rNOmax-N= 0.567 g NO3-N/g VS. d, K*NO3-N = 1.4 mg NO3-N/1 and K*CODVFA = 3.0 mg CODVFA/l. The stoichiometric consumption ratio between soluble COD and nitrate was found to be 4.5 ± 0.6 g CODs/g NO3-N. The specific growth rate was μ = 0.61 ± 0.12 d-t and the yield coefficient was YCOD = 0.22 ±0.04 g VS/g COD. [ABSTRACT FROM AUTHOR]

Sulphate was reduced via sulphide to sulphur when operating a single-stage completely mixed reactor configuration feeding synthetic feed.The aim of this study was to determine the volumetric and specific sulphate reduction rates using sugar, ethanol and methanol as a carbonand energy sources. The presented results indicated that sugar and ethanol were found to be suitable carbon and energy sources resulting in a volumetric and a specific sulphate reduction rate of 10.4 and 4.8 g SO4/(l.d) and 0.8 and 2.8 g SO4/(gVSS.d), respectively, at a Hydraulic Retention Time (HRT) of 3.6 h and at ambient temperature (21 deg. C). Methanol induced methanogenesis rather than sulphidogenesis. The experimental sulphide/sulphate ratio was consistently lower than the theoretical value which indicated that part of the formed sulphide was oxidized to sulphur. [ABSTRACT FROM AUTHOR]

Efficient nitrogen removal in a pre-denitrifying activated sludge process strongly depends on the amount anil nature of the carbon sourcein the wastewater. If denitrification has to be supported at periods, the response to a supplemental carbon source should be immediate and substantial. The aim of this work was to study how intermittent addition of ethanol affects process performance and the denitrifying capacity of the biomass in a pre-denitrifying activated sludge process. The investigated intermissions simulated a possible operational situation with a short stop of ethanol addition or a strategy with addition only at weekends. The long-term effect of intermittent addition wasalso studied. Experiments were performed in a pilot-scale activated sludge plant. Effluent nitrate was measured on-line and potential denitrification rates were determined with the acetylene inhibition technique. Once the bacteria were adapted to the external carbon source, the studied intermission of 24 hours as well as an intermission of six days showed no severe effect on denitrification capacity of the sludge. In order to maintain process stability with intermittent addition, the denitrifying bacteria had to sustain a high capacity at each stop. Five weeks of intermittent addition of ethanol did not change the level of nitrate reduction in the system during periods of ethanol addition. Denitrification potential was, however, negatively affected. The results suggest that it is possible to use an intermittent strategy when adding ethanol as an external carbon source in a pre-denitrifying system and for instance only support the denitrifying bacteriaduring weekends. (c) 1998 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]