Ultrasonic-pretreated waste activated sludge hydrolysis and volatile fatty acid accumulation under alkaline conditions: Effect of temperature

The effect of temperature on the hydrolysis and acidification of ultrasonic-pretreated waste activated sludge (WAS) under alkaline conditions was investigated in this study. The experiment temperatures were set at 10, 20, 37, and 55°C. Experimental results showed that the hydrolysis of ultrasonic-pretreated WAS under alkaline conditions increased significantly with temperature from 10 to 55°C, while the volatile fatty acid (VFA) accumulation was not augmented as temperature increased. Among the four temperatures tested, 37°C was the point with the highest VFA accumulation after 72h fermentation. VFA accumulation decreased markedly at 55°C compared to 37°C. Mechanism investigation revealed that among all the temperatures tested, 37°C was the temperature at which consumptions of WAS protein and carbohydrate, activities of key enzymes related to VFA formation and ratio of Bacteria to Archaea all reached the maximum. Due to activities of related microorganisms inhibited by higher temperature (55°C), VFA accumulation decreased at 55°C.     

Inhibition by fatty acids during fermentation of pre-treated waste activated sludge

Fermentation of waste activated sludge produces volatile fatty acids (VFAs), which can be used as the carbon sources for numerous biological processes. However, product inhibition can limit extent of fermentation to VFAs. In this study, product inhibition during fermentation of waste activated sludge pre-treated by a thermal hydrolysis process (THP-WAS) was investigated. Product inhibition was confirmed as spiking reactors with high levels of a mix of VFAs prevented fermentation taking place. Various inhibition models were trialled and it was found that a threshold model (based on thermodynamics) provided the best fit between model and data. This is the first time that threshold type inhibition has been shown for a mixed substrate, mixed population system. Batch fermentations carried out with THP-WAS of different dilutions were used to evaluate the impact of different organic loadings. The threshold VFA concentration for the systems studied was determined to be 17±1gCOD(VFA)L(-1). Inhibition was shown to be due to the presence of a combination of VFAs containing 2-6 carbon atoms each. When evaluated individually, by spiking individual VFAs, all VFAs except for acetate had the same impact at this threshold; acetate being approximately 50% as inhibitory as the other organic acids (COD basis). Based on this, a weighted model could be proposed to better represent the data. Strategies to improve overall yield could be increased production of acetate, or dilution to below the inhibitory level.     

Influence of pH and temperature on soluble substrate generation with primary sludge fermentation

The study was undertaken to evaluate the effect of pH and temperature control on the generation of soluble fermentation products from primary sludge. The effect was tested by running parallel experiments under pH and temperature controlled and uncontrolled conditions. In fermentation experiments conducted at 20 degrees C without pH control, the average soluble COD release was 14 mg per liter of wastewater treated, representing a potential increase of 5% in the biodegradable COD content of the primary sedimentation effluent. The corresponding average VFA generation was 9.2mg COD l(-1). The nutrient release was practically negligible and stayed at 0.4 mg l(-1) for nitrogen and 0.1mg l(-1) for phosphorus. Acetic acid accounted more than 45% of the generated VFA in all experimental runs. The acetic acid content of the VFA decreased with increasing initial VSS concentrations and higher pH levels. VFA generation by fermentation was significantly affected with temperature and pH control. Temperature change between 10 and 24 degrees C induced a five-fold increase in VFA generation, from 610 mg l(-1) at 10 degrees C to 2950 mg l(-1) at 24 degrees C.     

Anaerobic hydrolysis and acidification of organic substrates: determination of anaerobic hydrolytic potential

This study aimed to develop a biochemical-test mainly to evaluate the hydrolytic-potential of different substrates and to apply this test to characterize various organic substrates. Outcome of this study can be used for optimization of the WWTPs through enhancement of N/P removal or anaerobic digestion. Out of four series of batch experiments, the first two tests were conducted to determine the optimal operating conditions (test duration, inoculum-ratio etc.) for the hydrolytic-potential test using secondary and synthetically-prepared sludges. Based on the results (generation of CODs, pH and VFA), test duration was fixed between 6 and 7 d allowing to attain maximum hydrolysis and to avoid methanogenesis. Effect of inoculum-ratios on acid fermentation of sludge was not significantly noticed. Using this methodology, third and fourth tests were performed to characterize various organic substrates namely secondary, pre-treated sludge, pig and two different cattle slurries. VFA production was shown to be substantially dependent on substrates types.     

Biological sludge reduction and enhanced nutrient removal in a pilot-scale system with 2-step sludge alkaline fermentation and A2O process

To enhance nutrient removal performance and reduce disposal amount of waste activated sludge (WAS), a pilot-scale continuous system consisting of a 2-step sludge alkaline fermentation process and an A²O reactor was proposed. The feasibility of WAS reducing and resourcing by alkaline fermentation was investigated. Volatile fatty acids (VFA) yield was higher under alkaline condition than that under acidic condition. Through 2-step alkaline fermentation, substantial VFA was accumulated, and then elutriated out continuously from an up-flow column by domestic wastewater. The results showed that 38.2% of sludge was hydrolyzed, 19.7% was finally acidified into VFA, and as high as 42.1% of WAS was reduced. Moreover, after introducing the fermentation liquids with higher proportion of acetic acid and propionic acid into the A²O reactor, the total nitrogen and phosphorus removal efficiencies reached to 80.1% and 90.0%, respectively. Sludge reduction and enhanced nutrient removal could be achieved simultaneously in the proposed system.     

Biogas plasticization coupled anaerobic digestion: batch test results

Biogas has unique properties for improving the biodegradability of biomass solids during anaerobic digestion (AD). This report presents batch test results of the first investigation into utilizing biogas plasticization to "condition" organic polymers during active digestion of waste activated sludge (WAS). Preliminary design calculations based on polymer diffusion rate limitation are presented. Analysis of the 20 degrees C batch test data determined the first order (k(1)) COD conversion coefficient to be 0.167 day(-1) with a maximum COD utilization rate of 11.25 g L(-1) day(-1). Comparison of these batch test results to typical conventional AD performance parameters showed orders of magnitude improvement. These results show that biogas plasticization during active AD could greatly improve renewable energy yields from biomass waste materials such as MSW RDF, STP sludges, food wastes, animal manure, green wastes, and agricultural crop residuals.     

Mesophilic anaerobic treatment of sludge from saline fish farm effluents with biogas production

The mesophilic anaerobic treatment of sludge from saline fish farm effluents (total solids (TS): 8.2-10.2 wt%, chemical oxygen demand (COD): 60-74 g/l, sodium (Na): 10-10.5 g/l) was carried out in continuously stirred tank reactors (CSTRs) at 35 degrees C. COD stabilization between 36% and 55% and methane yields between 0.114 and 0.184 l/g COD added were achieved. However, the process was strongly inhibited, presumably by sodium, and unstable, with propionic acid being the main compound of the volatile fatty acids (VFA). When diluting the sludge 1:1 with tap water (Na: 5.3 g/l), the inhibition could be overcome and a stable process with low VFA concentrations was achieved. The results of the study are used to make recommendations for the configuration of full-scale treatment plants for the collected sludge from one salmon farming licence and to estimate the energy production from these plants.     

Comparison of laboratory-scale thermophilic biofilm and activated sludge processes integrated with a mesophilic activated sludge process

A combined thermophilic-mesophilic wastewater treatment was studied using a laboratory-scale thermophilic activated sludge process (ASP) followed by mesophilic ASP or a thermophilic suspended carrier biofilm process (SCBP) followed by mesophilic ASP, both systems treating diluted molasses (dilution factor 1:500 corresponding GF/A-filtered COD (COD(filt)) of 1900+/-190 mgl(-1)). With hydraulic retention times (HRTs) of 12-18 h the thermophilic ASP and thermophilic SCBP removed 60+/-13% and 62+/-7% of COD(filt), respectively, with HRT of 8 h the removals were 48+/-1% and 69+/-4%. The sludge volume index (SVI) was notably lower in the thermophilic SCBP (measured from suspended sludge) than in the thermophilic ASP. Under the lowest HRT the mesophilic ASP gave better performance (as SVI, COD(filt), and COD(tot) removals) after the thermophilic SCBP than after the thermophilic ASP. Measured sludge yields were low (less than 0.1 kg suspended solids (SS) kg COD(filt removed)(-1)) in all processes. Both thermophilic treatments removed 80-85% of soluble COD (COD(sol)) whereas suspended COD (COD(susp)) and colloidal COD (COD(col)) were increased. Both mesophilic post-treatments removed all COD(col) and most of the COD(susp) from the thermophilic effluents. In conclusion, combined thermophilic-mesophilic treatment appeared to be easily operable and produced high effluent quality.     

Acid and alkaline treatments for enhancing the growth of rhizobia in sludge

Wastewater sludges have been proposed as an effective media for the production of rhizobia. The effect of total suspended solid (TSS) concentrations and pretreatments of sludge on the growth of Sinorhizobium meliloti were investigated. Acid (pH 2.0-6.0 obtained with H2SO4) and alkaline (50-200 mequiv.wt./L of NaOH) treatments were applied to enhance the biodegradability of primary (0.325%-3.2% TSS obtained by dilution of original sample) and secondary (0.2%-0.4% TSS obtained by concentration of original sample) sludges. In primary sludge without pretreatment, the highest cell count (11.10 x 10(9) cfu/mL) was obtained with 1.3% TSS. However, a maximum cell count of 13.00 x 10(9) cfu/mL was reached using an acid treatment of pH 2.0 and a 0.325% TSS concentration. Moreover, the alkaline treatment with 100 mequiv.wt./L of NaOH and 0.65% TSS increased the cell yield to 21.00 x 10(9) cfu/mL. For secondary sludge without pretreatment, no enhancement of growth was observed while increasing TSS concentration. This may be due to the increase of inhibitory substances, such as heavy metals, and of the Ca and Mg concentrations. As in primary sludge, some acid and alkaline treatments of secondary sludge tend to improve the cell count of S. meliloti. However, the highest value of 9.80 x 10(9) cfu/mL obtained with 0.4% TSS at pH 2.0 was lower than that obtained with primary sludge. It was also observed that S. meliloti grown in treated sludges maintained its capacity to nodulate alfalfa.     

Continuous detoxification, transformation, and degradation of nitrophenols in upflow anaerobic sludge blanket (UASB) reactors

The anaerobic transformation and degradation of nitrophenols by granular sludge was investigated in upflow anaerobic sludge blanket (UASB) reactors continuously fed with a volatile fatty acid (VFA) mixture as the primary substrate. During the start-up, subtoxic concentrations of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2, 4-dinitrophenol (2, 4-DNP) were utilized. 4-NP and 2, 4-DNP were readily converted to the corresponding aromatic amine; whereas 2-NP was converted to nonaromatic products via intermediate formation of 2-aminophenol (2-AP). These conversions led to a dramatic detoxification of the mononitrophenols because the reactors treated the nitrophenolics at the concentrations which were over 25 times higher than those that caused severe inhibition. VFA removal efficiencies greater than 99% were achieved in both reactors at loading rates greater than 11.4 g COD per liter of reactor volume per day even at volumetric loading of mononitrophenols up to 910 mg/L . d.The sludges obtained from each of the reactors at the end of the continuous experiments were assayed for their specific nitrophenol reducing activity in the presence of different primary substrates. Reduction rates of 45 and 26 mg/g volatile suspended solids per day were observed for 2-NP and 4-NP, respectively, when utilizing the VFA mixture as primary substrate. Hydrogen, an interspecies-reduced compound, and substrates that provide interspecies-reducing equivalents-such as butyrate, propionate, and ethanol stimulated nitrophenol reduction, whereas acetate and methanol did not. Anaerobic batch biodegradability tests with the 2-NP-adapted sludge revealed that its corresponding aromatic amine, 2-AP, was degraded to methane at a specific rate of 14.5 mg/g VSS . d. Acetate was observed to be the major intermediate during 2-AP degradation in the presence of a specific methanogenic inhibitor 2-bromoethanesulfonate. The results of this study indicate that UASB reactors can be applied to rapidly detoxify and, under certain circumstances, degrade nitroaromatic compounds. (c) 1996 John Wiley & Sons, Inc.     

Effect of long-term cobalt deprivation on methanol degradation in a methanogenic granular sludge bioreactor

The effect of the trace metal cobalt on the conversion of methanol in an upflow anaerobic sludge bed (UASB) reactor was investigated by studying the effect of cobalt deprivation from the influent on the reactor efficiency and the sludge characteristics. A UASB reactor (30 degrees C; pH 7) was operated for 261 days at a 12-h hydraulic retention time (HRT). The loading rate was increased stepwise from 2.6 g chemical oxygen demand (COD) x L reactor(-1) x d(-1) to 7.8 g COD x L reactor(-1) x d(-1). Cobalt deprivation had a strong impact on the methanogenic activity of the sludge. In batch tests, the methanogenic activity of the sludge with methanol as the substrate increased 5.3 (day 28) and 2.1 (day 257) times by addition of 840 nM of cobalt. The sludge had an apparent K(m) for cobalt of 948 nM after 28 days of operation and 442 nM at the end of the run. Cobalt deprivation during 54 days of operation led to a methanol conversion efficiency of only 55%. Continuous addition of cobalt (330 nM) for 33 days improved the methanol removal efficiency to 100%. In this period of cobalt dosing, the cobalt concentration in the sludge increased 2.7 times up to 32 microg x g TSS(-1). Upon omission of the cobalt addition, cobalt washed-out at a stable rate of 0.1 microg x g VSS(-1) x d(-1). At the end of the run, the cobalt concentration of the sludge was similar to that of the seed sludge.     

Anaerobic treatment of cassava starch extraction wastewater using a horizontal flow filter with bamboo as support

Small-scale sour starch agroindustry in Colombia suffer from absence of water treatment. Although starch processing plants produce diluted wastewater, it is a source of pollution and cause environmental problems to the nearby rural population. A laboratory scale anaerobic horizontal flow filter packed with bamboo pieces was evaluated for the treatment of cassava starch extraction wastewater. The wastewater used in the experimentation was the draining water of the starch sedimentation basin. The reactor was operated for 6 months. It was inoculated with a semi-granular sludge from an anaerobic UASB reactor of a slaughterhouse. Maximum organic loading rate (OLR) applied was 11.8g COD/L d without dilution of the wastewater. At steady state and maximum OLR applied, 87% of the COD was removed and a gas productivity of 3.7L/L d was achieved. The average biogas yield was 0.36L/g COD removed. Methane content in the biogas was in the range of 69-81%. The total suspended solids (TSS) removed were 67%. The relative high lactic acid content did not negatively influence the performance of the reactor. No perturbation due to cyanide (3-5mg/L) was observed during the reactor operation. The results obtained indicated that the anaerobic horizontal flow filter could be used efficiently for the treatment of wastewater from Colombian starch processing small-scale agroindustry.     

Occurrence of Listeria sp and L monocytogenes in sewage sludge used for land application: effect of dewatering,liming and storage in tank on survival of Listeria species

The application of sewage sludge to agricultural land is widely used in France. To determine the impact of sludge treatments, concentrations of Listeria sp., Listeria monocytogenes and faecal indicators were monitored in five types of sludge from three sewage treatment plants in Angers (France) and its suburbs over a 1-year period. On the whole, bacteria were reduced in numbers through sludge treatments. Apart from liming, which leads to reduced levels of bacteria below detection limits, other sludge treatments did not eliminate Listeria sp. and faecal indicators. Listeria sp. and L. monocytogenes were found respectively in 87% and 73% of dewatered sludges and in 96% and 80% of sludges stored in tanks. Concentrations of L. monocytogenes, ranging from 0.15 to 20 MPN g(-1) dry matter in dewatered sludge and from 1 to 240 MPN g(-1) dry matter in sludge stored in tanks, did not show seasonal variations. Spreading of sanitised sludge onto agricultural land results in the addition of 10(6)-10(8) L. monocytogenes per hectare per year, which may contribute to the increase in the dissemination of this pathogenic species in the environment.     

Anaerobic treatment of highly concentrated aniline wastewater using packed-bed biofilm reactor

The performance of packed-bed biofilm reactor (PBBR) with self-floating bio-carriers was investigated to treat highly concentrated organic nitrogenous aniline wastewater with a COD value as high as 24,000 mg/L. With 45 vol% of carrier charge inside the reactor, the aniline wastewater can be effectively treated with 94% of COD removal efficiency at a low organic loading rate (OLR) of 0.9 kg COD/(m³ d). The removal efficiency decreased gradually down to 75% when OLR increased to 12.27 kg COD/(m³ d) that corresponded to 1 day of HRT. Separate tests with biofilm alone showed that the conversion contribution of the biofilm was about half of the overall COD conversion by the biofilm plus sludge system at the same OLRs of 3–4 kg COD/(m³ d), and that the biofilm had higher activity than suspended sludge. Ammonium released from decomposed aniline was increased gradually from 500 to 1700 mg/L with the OLR increase from 0.9 to 12.27 kg COD/(m³ d), which resulted in inhibitory effect to the microorganism due to the toxicity of free ammonia. Batch anaerobic toxicity tests showed that the biofilm was less sensitive to toxic compounds than suspended sludge and could tolerate higher concentration of free ammonia.     

Volatile fatty acids productivity by anaerobic co-digesting waste activated sludge and corn straw: Effect of feedstock proportion

Volatile fatty acids (VFAs) are the most suitable and biodegradable carbon substrates for many bioprocesses. This study explored a new approach to improve the VFAs production from anaerobic co-digesting waste activated sludge (WAS) with corn straw (CS). The effect of feedstock proportion on the acidification efficiency was investigated. The maximum VFAs yield (corresponding fermentation time) was substantially increased 69% (96 h), 45% (72 h), 13% (120 h) and 12% (120 h) with 50%, 35%, 25% and 20% CS proportion of feedstock, respectively. HAc (acetic acid) was consistently the most abundant, followed by HPr (propionic acid) and n-HBu (butyric acid) in the co-digesting tests. The increase of CS in feedstock led to more production of HAc and HPr. Moreover, the consumption of protein and carbohydrate were also improved remarkably from 2955 and 249 mg COD/L (individual WAS fermentation) to 6575 and 815 mg COD/L (50%_WAS:50%_CS co-digestion) from 120 onward, respectively. The highest contribution of CS to additional VFAs production was1113 mg VFAs (as COD)/g CS/L in the 65%_WAS:35%_CS co-digesting test. Our study indicated a valuable method to improve VFAs production from anaerobic co-digesting WAS and CS.     

Production of polyhydroxyalkanoates by activated sludge treating a paper mill wastewater

Production of polyhydroxyalkanoates (PHAs) in activated sludge treating wastewater represents an economical and environmental promising alternative to pure culture fermentations. A process for production of PHA from a paper mill wastewater was examined at laboratory scale. The three stage process examined consisted of acidogenic fermentation to convert wastewater organic matter to volatile fatty acids (VFAs), an activated sludge system operating under feast/famine conditions to enrich for PHA producing organisms and accumulation of PHA in batch experiments. After fermentation of the wastewater, 74% of the soluble COD was present as VFA (acetate, propionate, butyrate and valerate) and the resulting PHA after batch accumulation consisted of 31-47 mol% hydroxybutyrate and 53-69 mol% hydroxyvalerate. The maximum PHA content achieved was 48% of the sludge dry weight and the three stage process exhibited a potential to produce 0.11 kg of PHA per kg of influent COD treated.     

Development of thermophilic methanogenic sludge in compartmentalized upflow reactors

The characteristics and development of thermophilic anaerobic sludge in upflow staged sludge bed (USSB) reactors were studied. The compartmentalized reactors were inoculated with partially crushed mesophilic granular sludge and then fed with either a mixture of volatile fatty acids (VFA) or a mixture of sucrose and VFA. The staged degradation of the soluble substrate in the various compartments led to a clear segregation of specific types of biomass along the height of the reactor, particularly in reactors fed with the sucrose-VFA mixture. Both the biological as well as the physical properties of the cultivated sludge were affected by the fraction of nonacidified substrate. The sludge in the first compartment of the reactor treating the sucrose-VFA mixture was whitish and fluffy, most likely resulting from the development of acidifying bacteria. Sludge granules which developed in the top part of this reactor possessed the highest acetogenic and methanogenic activity and the highest granule strength as well. The experiments also revealed that the conversion of the sucrose-VFA mixture into methane gradually deteriorated at prolonged operation at high organic loading rates (50 to 100 g COD . L(-1) . day(-1)). Stable long-term performance of a reactor can only be achieved by preserving the sludge segregation along the height of the reactor. In the reactor fed solely with the VFA mixture little formation of granular sludge occurred. In this reactor, large differences in sludge characteristics were also observed along the reactor height. Li(+)-tracer experiments indicated that the hydraulic regime in the USSB reactor is best characterized by a series of at least five completely mixed reactors. The formation of granular sludge was found to influence the liquid flow pattern. (c) 1996 John Wiley & Sons, Inc.     

Effect of temperature on low-strength wastewater treatment by UASB reactor using poly(vinyl alcohol)-gel carrier

The feasibility of treating low-strength wastewater with an up-flow anaerobic sludge blanket (UASB) reactor, using a poly(vinyl alcohol)-gel carrier, at various temperatures and hydraulic retention times (HRTs) was examined. The temperature was decreased from 35°C to 25°C and then to 15°C. The HRT was reduced from 2.0 h to 0.22 h. The COD removal rate reached 28 kg-COD m(-3)d(-1) at 35°C, 16 kg-COD m(-3)d(-1) at 25°C, and 6 kg-COD m(-3)d(-1) at 15°C. The COD removal rate was reduced by half for each temperature reduction of 10°C.     

Carbon and nitrogen substrates consumption, ammonia release and proton transfer in relation with growth of Geotrichum candidum and Penicillium camemberti on a solid medium

The influence of hydraulic retention time (HRT) and gelatin concentration on the acidification of gelatinaceous wastewater in an upflow anaerobic reactor was investigated at pH 5.5 and 37 degrees C. The degree of gelatin degradation increased with the HRT, from 84.1% at 4 h to 89.6% at 24 h, but decreased with the increase of the gelatin concentration in the influent from 65.2% at 2 g-CODl(-1) to 51.9% at 30 g-CODl(-1). The degradation of gelatin followed the Monod kinetics with a maximum rate of 1.10 g (g-VSS x d)(-1) and a half-rate constant of 0.23 gl(-1). The overall production rate of VFA and alcohols decreased with HRT, from 0.33 g (g-VSS x d)(-1) at 4 h to 0.15 g (g-VSS x d)(-1) at 24 h, but increased with gelatin concentration in the influent, from 0.10 g (g-VSS x d)(-1) at 4 g-CODl(-1) to 0.58 g (g-VSS x d)(-1) at 30 g-CODl(-1). The key acidification products were acetate, propionate and butyrate, plus i-butyrate, valerate, i-valerate, caproate and ethanol in smaller quantities. Formate, methanol, propanol and butanol were found only in certain runs. Only 4.5-7.8% of COD in wastewater was converted to hydrogen and methane. The sludge yield was estimated as 0.320+/-0.014 g-VSS (g-COD)(-1).     

Anaerobic acidogenesis of primary sludge: the role of solids retention time

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate. (c) 1994 John Wiley & Sons, Inc.