Hydraulic Shock Loads Research Articles

Integrated model of the production of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in anaerobic chemostats during transient conditions

A model to predict the accumulation of soluble microbial products (SMP) in anaerobic chemostats during steady-state and transient conditions is presented in this paper. The model incorporates the concept of production and degradation of extracellular polymeric substances (EPS or ECP) as part of SMP, and was used to predict SMP production during hydraulic and organic shock load experiments in anaerobic continuously stirred tank reactors (CSTRs). For most variables the model predicted reasonably well the shock loads, and the best-fit values of the main parameters provided valuable information on the types of SMP that predominate under particular culture conditions. According to the model, during steady-state conditions ∼58% of the SMP are utilization-associated products (UAP) whilst ∼42% are biomass-associated products (BAP) of which ∼7% are soluble EPS (sEPS). During the hydraulic and organic shock loads the importance of BAP and sEPS decreases and the UAP accounts for up to 95% of the SMP.

Cultivation, granulation and characteristics of anaerobic ammonium-oxidizing sludge in sequencing batch reactor

Anaerobic sequencing batch reactor (SBR) was started-up by inoculating the nitrifying activated sludge. After an operation of 72 d, the bioreactor reached at steady state with ammonia and nitrite removal percentages higher than 95%. During operation, the sludge granulated in the reactor. The morphology and internal structure of sludge granules changed conspicuously, the density increased while the color changed from khaki to red. The average granular diameter grew from 1.2 to 3.69 mm, and its settling velocity accelerated from 107.68 to 118.49 m/h. Sludge granulation improved the tolerance to hydraulic shock loading, and reduced sludge washout (TSS < 0.028 g/L). The dominant bacterial communities (filamentous and cocci) in nitrifying activated sludge were replaced by irregular shaped ANAMMOX bacterial species gradually. An increase of ANAMMOX rate was achieved with the increasing granular diameter. SBR is a useful reactor to cultivate ANAMMOX granular sludge, while granular ANAMMOX sludge thus developed can be used as seeding sludge in a pilot-scale or full scale wastewater treatment plant.

The effects of hydraulic and organic shock loads on the robustness of upflow anaerobic sludge blanket reactors treating sewage

In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic shock loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to shock loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic shock load, or prior to the shock, a sufficient amount of sludge needs to be discharged from the reactor.

Simultaneous carbon, nitrogen and phosphorous removal from municipal wastewater in a circulating fluidized bed bioreactor

In this study, the performance of the circulating fluidized bed bioreactor (CFBB) with anoxic and aerobic beds and employing lava rock as a carrier media for the simultaneous removal of carbon, nitrogen and phosphorus from municipal wastewater at an empty bed contact time (EBCT) of 0.82 h was discussed. The CFBB was operated without and with bioparticles’ recirculation between the anoxic and aerobic bed for 260 and 110 d respectively. Without particles’ recirculation, the CFBB was able to achieve carbon (C), total nitrogen (N) and phosphorous (P) removal efficiencies of 94%, 80% and 65% respectively, whereas with bioparticles’ recirculation, 91%, 78% and 85% removals of C, N and P were achieved. The CFBB was operated at long sludge retention time (SRT) of 45–50 d, and achieved a sludge yield of 0.12–0.135 g VSS g COD −1. A dynamic stress study of the CFBB was carried out at varying feed flow rates and influent ammonia concentrations to determine response to shock loadings. The CFBB responded favourably in terms of TSS and COD removal to quadrupling of the feed flow rate. However, nitrification was more sensitive to hydraulic shock loadings than to doubling of influent nitrogen loading.

Particle detachment during hydraulic shock loads in granular media filtration

Particle breakthrough can occur by either the breakoff of previously captured particles (or flocs) or the direct passage of some influent particles through the filter. Filtration experiments were performed in a laboratory-scale filter using spherical glass beads with a diameter of 0.55 mm as collectors. A single type of particle suspension (Min-U-Sil 5) and three different destabilisation methods (pH control, alum and polymer destabilisation) were used to destabilise particles. The filtration velocity of 5 m/h was similar to that used in standard media filtration practice. To assess the possibility of particle detachment during normal filtration, a hydraulic shock load (20% increase of flow rate) was applied after 4 h of normal filtration. The magnitude of particle detachment was proportional to the particle size for non-Brownian particles. At the same time, less favourable particles, i.e. particles with larger surface charge, were easily detached during the hydraulic shock load. Therefore, proper particle destabilisation before filtration is crucial for maximum particle removal, as well as minimum particle breakthrough.

Long-term simulation of the activated sludge process at the Hanover-Gümmerwald pilot WWTP

The aim of this study was to obtain a validated model, consisting of the Activated Sludge Model No. 3 (ASM3) and the EAWAG bio-P module, which could be used as a decision tool for estimating the maximum allowable peak flow to wastewater treatment plants during stormwater conditions. The databases used for simulations originated from the Hanover-Gümmerwald pilot plant subjected to a series of controlled, short-term hydraulic shock loading experiments. The continuous influent wastewater composition was generated using on-line measurements of only three parameters (COD, N-NH 4 +, P-PO 4 3−). Model predictions were compared with on-line data from different locations in the activated sludge system including the aerobic zone (concentrations of N-NH 4 +, N-NO 3 −) and secondary effluent (concentrations of P-PO 4 3−). The simulations confirmed experimental results concerning the capabilities of the system for handling increased flows during stormwater events. No (or minor) peaks of N-NH 4 + were predicted for the line with the double dry weather flowrate, whereas peaks of N-NH 4 + at the line with the quadruple dry weather flowrate were normally exceeding 8 g N m −3 (similar to the observations).

Moving bed biofilm reactors: a small-scale treatment solution

The design and operational suitability of the moving bed process for small-scale sewage treatment systems were evaluated. A prototype plant was installed at a new housing development near Winchester, UK, and operated under different conditions over an eight-month period. During normal operation, the MBBR plant produced a good quality effluent with average values for BOD5, COD, SS and NH4-N of 15.6 mg l(-1), 65.9 mg l(-1), 21 mg l(-1) and 4.7 mg l(-1), respectively. The plant was further subjected to organic and hydraulic shock loads. The treatment performance remained high over the organic shock period, however, hydraulic surges of up to 10 times the design flow caused a loss of solids from the final settlement stage. While organic carbon removal resumed to over 80% within a single week after a prolonged power failure, effluent NH4-N values remained high for a period of three weeks. Besides producing a good quality effluent, the MBBR plant proved to be simple and reliable to operate, thus providing a viable treatment solution for small-scale applications.

The Effect of Organic and Hydraulic Shock Loads on the Production of Soluble Microbial Products in Anaerobic Digesters

Anaerobic chemostats were used to investigate the effects of organic and hydraulic shock loads on the production of soluble microbial products (SMP). Production of SMP was found to increase during glucose spikes, reaching up 15% of the influent chemical oxygen demand. These SMP appear to be utilization-associated products produced as a result of the temporarily high organic load, and chemical analysis and ultrafiltration experiments revealed that most of these compounds are difficult to identify and that the majority of them are present in the low molecular weight (MW) range. Production of SMP also increased when the hydraulic retention time was reduced from 15 to 3 days, and an increase in DNA concentration in the bulk solution suggested enhanced cell lysis. Although the cause of lysis was not clear, it is believed that most of the SMP produced under such conditions were biomass-associated products following cell death. While the majority of these compounds lay in the low MW range, as much as 35% were found to have MWs greater than 1 kDa. During the period when the anaerobic chemostat was fed no alkalinity and the pH remained lower than 6.5 for more than a week, a slightly higher production of SMP and a shift in the MW distribution towards the production of higher MW SMP was observed.

Effect of soluble organic, particulate organic, and hydraulic shock loads on anaerobic sequencing batch reactors treating slaughterhouse wastewater at 20 °C

Anaerobic sequencing batch reactors (ASBRs) treating slaughterhouse wastewater at 20 °C were subjected to soluble organic, particulate organic and hydraulic shock loads. The normal organic loading rate (OLR) was increased by a factor ranging from 1.5 to 3.6. During the soluble organic shock load, effluent soluble chemical oxygen demand (SCOD), volatile fatty acid (VFA), and suspended solids (SS) concentrations increased from averages of 200, 58 and 249 mg/l, respectively, in control reactors to maxima of 5626, 1642 and 10 723 mg/l, respectively, in overloaded reactors. However, concentrations were rapidly reduced to pre-shock load levels shortly after normal operating conditions were resumed. The particulate and hydraulic shock loads had small and temporary effects on effluent SCOD and VFA concentrations, but high SS concentrations were observed in the effluent of most overloaded reactors. However, solids loss during effluent discharge did not significantly affect long-term performance of the ASBRs, probably because the sludge bed contained high initial volatile SS (VSS) concentration (21.9 ± 3.2 g/l), and also a fraction of the VSS removed from the reactors during effluent discharge was composed of undegraded colloidal solids fed with the substrate, as opposed to bacterial flocs. Nevertheless, maintaining high VSS concentrations in the sludge bed will probably prevent long-term negative effect of biomass loss during sudden shock loads.

Effect of rapid hydraulic shock loads on the performance of granular bed baffled reactor

This paper describes the performance of a granular bed baffled reactor when receiving unpredictable hydraulic shock loads, which is a frequent occurrence in industrial wastewater treatment plants. Shock loads were created by rapidly increasing volumetric organic loading rates from 2.5 to 20 kg COD m−3 d−1, by decreasing (in a stepwise fashion) hydraulic retention time from 48 firs to 6 his. Synthetic wastewater containing glucose as the main organic compound was used in this study. High effluent quality was observed, with soluble COD removal efficiencies of 94% to 97%, during all shock loading conditions at steady state. The reactor appeared to possess high tolerance to rapid hydraulic changes with fast recovery time. Marked phase separation between different microorganisms occurred at high organic loading rate, with addogenesis and methanogenesis being the respective dominant activities in the upstream and downstream compartments of the reactor. The compartmentalised nature of the reactor and the granular bed structure were believed to be responsible for high reactor stability during overloading conditions. Microbial ecology in the system appeared to favour acetate and butyrate production at high organic loading rate. Granular biomass possessed good settling characteristics, hence encouraging high biomass retention within the system. The dense granular bed in the methanogenic zone acted as a filtration bed for lighter floating non‐granular biomass, thus further reducing overall effluent solids concentration. This study demonstrated that the granular bed baffled reactor is a suitable system for treating industrial wastewaters with highly varying flow rates

Influence of hydraulic shock loads and TDS on the performance of large-scale CETPs treating textile effluents in India

The present study relates to the influence of hydraulic shock loads and total dissolved solids (TDS) on the performance of three large-scale common effluent treatment plants (CETPs) treating textile effluents, which is generated from clusters of small-scale industries in the state of Rajasthan in India. Of the three CETPs, two having capacities 7.0 and 9.0 million liters per day (mld) are located in Pali and one of capacity 6.0 mld in Balotra, District Barmer. Wastewater from about one thousand small-scale industries is treated in these CETPs. The effects of hydraulic shock loads and TDS on effluent data from secondary clarifier for parameters biochemical oxygen demand (BOD) and suspended solids (SS) for CETPs at Pali, and chemical oxygen demand (COD) and SS for the CETP at Balotra were studied. It was observed that the effluent BOD and SS remained within the prescribed limits for CETP Pali at 30% increased flow rate, whereas effluent COD and SS at 30% increased flow rate for CETP Balotra exceeded the prescribed limits and the CETP could sustain 20% increased flow rate. The shock loading analysis revealed that CETP Balotra had reduced capacity to sustain shock loads by 10% as compared to CETP Pali due to the presence of high TDS (15 000–20 000 mg/l). High TDS interfered with the oxygen transfer necessary for biological metabolism, thereby affected the efficiency of activated sludge process. Hence, activated sludge process treating high TDS effluents are more sensitive to hydraulic shock loads and prone to process upsets.

The effect of temperature on slaughterhouse wastewater treatment in anaerobic sequencing batch reactors

Treatment of a low strength complex wastewater of chemical oxygen demand (COD) around 500 mg/L was studied in a 10 L capacity laboratory scale anaerobic baffled reactor (ABR). It was operated at hydraulic retention times (HRTs) of 20, 15, 10, 8 and 6 h. Corresponding organic loading rates (OLRs) were 0.6, 0.8, 1.2, 1.5 and 2 kg COD/m3 d. At every HRT (or OLR), pseudo steady state (PSS) was achieved. Even at maximum OLR of 2 kg COD/m3 d, COD and biochemical oxygen demand (BOD) removals exceeded 88%. Removal of particulate fraction of organics was found to be greater than soluble fraction. Compartment-wise studies of various parameters revealed that if the OLR was larger, the number of initial compartments played significant role in the removal of organics. The values of volatile fatty acids (VFA) demonstrated that hydrolysis and acidogenesis were the main biochemical activities in the initial few compartments. Based on the tracer studies, dead space in the ABR was found to range from 23% to 34%. The flow pattern in the ABR was classified as intermediate between plug flow and perfectly mixed flows. Observations from scanning electron micrographs (SEM) also suggested that distinct phase separation takes place in an ABR. Study of organic and hydraulic shock loads revealed that ABR was capable of sustaining the type of shock loads generally experienced at a sewage treatment plant (STP).

Treatment of anaerobically pre-treated domestic sewage by a rotating biological contactor

The performance of a rotating biological contactor (RBC) for the post-treatment of the effluent of an up-flow anaerobic sludge blanket (UASB) was the subject of this study. Different hydraulic and organic loading rates have been investigated. The removal efficiencies of COD total, COD suspended, COD colloidal and COD soluble increased at a higher hydraulic retention time (HRT) and a lower influent organic loading rate. The results obtained indicated that a two-stage RBC reactor at an HRT of 10 h and an organic loading rate of 6.4 g COD m −2 d −1 represents an effective post-treatment process. Most COD suspended and COD colloidal were removed in the first stage while nitrification proceeded in the second stage. The overall nitrification efficiency was 92% at an ammonia loading rate of 1.1 g m −2 d −1. Total E. coli removal at HRTs of 10, 5 and 2.5 h were 99.5%, 99.0% and 89.0%, respectively. The major part of suspended E. coli (>4.4 μm) was removed by sedimentation or by adsorption in the biofilm of the first stage of RBC (99.66%). However, E. coli in the colloidal fraction (<4.4 to >0.45 μm) was eliminated in the second stage of RBC (99.78%). A comparison of the performance of a one-stage versus two-stage RBC system, operated at the same total loading rate, revealed an improvement in the effluent quality of the two-stage effluent as compared to the one-stage effluent. The two stages RBC were used to examine the effect of hydraulic shock loads on reactor performance in terms of COD, nitrification and E. coli removal.

Organic and Hydraulic Shock Loadings on a Biological Aerated Filter

The performance of a biological aerated filter (BAF) during short-term (60 min) organic and hydraulic shock loads was investigated. The BAF used for the present experiment was not capable of absorbing high peak organic shock loads when the organic loads were increased from a normal load of 1.2–1.4 kg soluble chemical oxygen demand (sCOD) m−3 d−1 to shock loads between 5.1– 7.3 kg sCOD m−3 d−1, based on empty bed volumes. Nevertheless, the effect on the biomass was limited as normal performance resumed very quickly. Increases in the hydraulic velocity from 0.7–1.0 m h−1 to 1.5–2.9 m h−1 had little effect on BAF performance in terms of soluble COD removal. Yet, sCOD effluent concentrations of <55 mg l−1 (~22 mg l−1 biochemical oxygen demand) were always achieved. The recovery of the reactor in both cases was fast, resuming normal performance within 60 min after the application of the shock load.

Influence of up-flow velocity on the performance of an anaerobic filter under oleic acid overloads

An upflow velocity of 0.21 m h−1 was optimal to minimize the effect of organic shocks (from 6 to 30 kg COD m−3 d−1) when operating an upflow anaerobic filter for the treatment of an oleic acid-based effluent (50% w/v COD). This value represented the transition between a mass transfer controlled regime and a kinetic regime. Under hydraulic shock loads, an increase in upflow velocity from 0.3 to 0.4m h−1 decreased the removal efficiency from 68 to 51%.

Removal of organics from wastewater using a novel biological hybrid system

This paper summarizes the results obtained using the hybrid aerated submerged fixed-film (HASFF) process. HASFF is an innovative system comprising a four-compartment reactor having an array of fixed ceramic plates maintained under diffused aeration to support attached biomass, with activated sludge recycle to promote suspended growth in the reactor. Wastewater from a municipal treatment plant was fed to the reactor and its activated sludge was used for recycling in the hybrid system. Four pilot units were operated in the plant at various hydraulic retention times, HRTs (2, 4, 6 and 8 h), using primary-settled wastewater under organic loading rates up to 0.7 g BOD/gMLTVS. d. Data obtained showed that the overall BOD percentage removal efficiencies were consistently above 94.0% at all HRTs including the 2 hours while the COD percentage removal efficiencies ranged between 65.7-76%. The effluent's mean filtered BOD concentration ranged between 4.5-7.5 mg/l whereas the mean filtered COD concentration ranged between 70.0-89.6 mg/l. Increasing the hydraulic loading rate by four-folds from 0.08 to 0.32 m3/m2.d had a minor effect on the unit's BOD and COD percentage removal efficiencies indicating a robust biological process that is resilient to hydraulic shock loads, thereby offering a viable upgrading option.

The effect of shock loads on the performance of an anaerobic baffled reactor (ABR). 2. Step and transient hydraulic shocks at constant feed strength

Two Anaerobic Baffled Reactors (ABR) were used to examine the effect of transient and step hydraulic shock loads on reactor performance in terms of chemical oxygen demand (COD) removal and microbial responses to hydraulic shocks in each compartment. The reactors were operated at 20-h hydraulic retention time (HRT), 4 g/litre COD and 35°C as a base-line condition. Hydraulic shocks with an HRT of 1 h (an increase of 20 times in the influent flowrate), 10 h and 5 h were applied to the reactors for 3 h, 2 weeks and 3.5 weeks, respectively, and a variety of key intermediates monitored over time in each compartment. The baseline conditions (4.8 kg-COD/m 3 d) resulted in 98% COD removal; however, when the HRT decreased to 10 h (9.6 kg-COD/m 3 d) removal dropped to 90%, and at 5-h HRT (19.2 kg-COD/m 3 d) removal was only 52%. It was found that the ABR was very stable to large transient shocks, and while biomass loss was substantial, it recovered back to its basline performance only 9 h after the shock ceased. Tracer studies found that the total dead space in the reactor at 24 g-VS/litre and 20-h HRT was about 18% by volume; however, when the HRT was reduced to 10 and 5 h, this increased to 39%. Comparison of this data with previous results for varying feed concentration and recycle ratio in the ABR revealed that removal efficiency could be tentatively explained in terms of HRT; organic loading rate; the concentration/activity and kinetics of the biomass; the dead space in the reactor; the severity and type of channelling in each compartment; the substrate concentration in each compartment driving mass transfer into the flocs; and floc size. Hence, it seems that this type of reactor configuration has potential in treating industrial wastes that vary in both flow and concentration, and still enable high removal rates to be achieved.

97/03889 Responses of an anaerobic fixed-film reactor to hydraulic shock loadings

97/03889 Responses of an anaerobic fixed-film reactor to hydraulic shock loadings

Responses of an anaerobic fixed-film reactor to hydraulic shock loadings

The responses of an anaerobic fixed-film reactor (AFFR) to hydraulic shock loadings were studied. The AFFR was started up with a synthetic wastewater of 3000 mg COD/l at 5.00 d hydraulic retention time (HRT), achieving 98.1% COD removal efficiency. When stable operation was attained, the HRT was sporadically adjusted to 2.50, 1.25, 1.00 and 0.50 d to simulate two, four, five and 10 times hydraulic shock loadings, respectively, while the COD loading was maintained constant. Under two, four and five times hydraulic shock loadings, the COD removal efficiency was temporarily reduced to between 84.4 and 88.3%, and the pH of the treated effluent and the biogas production were also affected. The AFFR could recover from the temporary inhibition due to these shock loadings and resumed normal operation within eight days. On the other hand, under 10 times hydraulic shock loading, the treatment performance deteriorated drastically. Volatile fatty acids (VFAs) accumulated in the AFFR liquor, resulting in reactor souring and failure. When the HRT was returned to 5.00 d, the biofilter could be recovered within a few days. The ability of the AFFR to recover from critical hydraulic shock loadings and system failure was attributed to the immobilized-biofilm design, which enabled the temporarily inhibited biofilms to be retained in the AFFR and regain activity when favourable conditions were restored.

Effects of hydraulic shock loads on small on-site sewage treatment unit

This research was to determine the effects of hydraulic shock loads by intermittent feeding on the removal efficiency of a small prefabricated real-sized septic tank/anaerobic filter unit. Besides the ‘control’ 24-hour continuous runs the other twice a day feeding periods covered 16, 12 and 8 hours per day, with the tank's retention time varying from 22.5 to 90 hours. It was demonstrated that the variation of the hydraulic feeding patterns ranging from 24-hour continuous feed to 8 h per day intermittent feed did not affect the performance of the system much. The percentage of BOD reduction was decreased from 85 to 82 and 81 percent for the feed times of 24, 16 and 8 hours per day, respectively. The tank capacity played a relatively major role in determining the removal efficiency of the process. The efficiency of BOD and SS reduction dwindled from 82.2 to 68.9 and 56.0% with the corresponding reduction in tank sizes from 90 to 45 and 22.5 hours retention, respectively. In any event, the unit could not satisfactorily remove nutrients. A retention period of not less than 48 hours is recommended if the Thai effluent standards are to be met. Equations for predicting the BOD removal capability were also developed.