Waste Activated Sludge Disintegration in an Ultrasonic Batch Reactor

The production of excess sludge is one of the most serious challenges in biological wastewater treatment. In the present work, disintegration is added as a new additional unit operation in a wastewater treatment plant, and the main objective is to reduce the amount of excess sludge. The use of high power ultrasound can effectively disintegrate the bacterial cells, and thereby, enhance the subsequent biodegradation during digestion. In the study, attempts are made to determine the disintegration capacity of waste activated sludge that has different total solids (TS) concentrations with low ultrasound frequency (20 kHz) and a fixed amplitude value (50%). The results show that in terms of soluble chemical oxygen demand (SCOD) release, sludge disintegration was primarily governed by ultrasonic density (W mL^–1), whereas specific energy input appears to be more critical for protein release. A SCOD release of about 329 mg SCOD gTS^–1 was obtained at a TS content of 2% and specific energy input of 5 kWs gTS^–1. The SCOD release decreased to 248.5 and 124.2 mgSCOD gTS^–1 at TS contents of 4 and 6%, respectively. The highest protein release of 80.7 mg gTS^–1 was obtained at a TS content of 2% and a specific energy input of 10 kWs g^–1. The sludge disintegration efficiency declined significantly at higher TS content.     

Das Entwässerungsverhalten von Klärschlamm in Gegenwart von Polyelektrolyten

Dewatering Behaviour of Sludge in the Presence of Polyelectrolytes Interactions of sludge particles with well defined synthetic polyelectrolytes of different charge, molecular mass, and molecular geometry were investigated by means of zeta- and streaming potential measurements and polyelectrolyte titrations. Different mechanisms of flocculation were discussed with regard to the dewatering behaviour of the sludge. In dependence on the flocculation procedure (cationic monoflocculation, anionic-cationic, and cationicanionic dual flocculation) as well as on the chain length and branching of the polyelectrolytes used, different mechanisms of sludge dewatering were discussed: Polyanions are not adsorbed on the sludge particles and lead to a decline of the dewatering results. Linear short chain polycations result in a flocculation after surface charge neutralization of the particles according to a patch mechanism. Long chain linear polycations cause a bridging of the particles leading to a flocculation without charge neutralization of the aggregates formed. With branched polycations, a flocculation according to a patch mechanism is observed. These polycations form sludge particle aggregates which are surface charge neutralized at the flocculation point. In anionic-cationic dual flocculations using long chain polycations, an inclusion flocculation due to polyanion-polycation complex formation is the predominating mechanism. The cationic-anionic dual flocculation with complete covering of the particles with polycations in the first step can be discussed by a patch mechanism quite similar to an anionic monoflocculation of cationic particles. By knowing the mechanism of interaction for a given flocculation agent, an optimal sludge dewatering procedure can be predicted.     

Effects of Fenton Pre‐Treatment on Waste Activated Sludge Properties

Fenton process was investigated for the purpose of biological sludge disintegration. The Box–Wilson experimental design was employed to evaluate the effects of major process variables (Fe(II) and H₂O₂ concentrations) on both disintegration and dewatering performance of sludge. Results showed that 4 g Fe(II)/kg total solids (TSs) and 60 g H₂O₂/kg TS are efficient for floc disintegration. Fenton pre‐treatment enhanced the biodegradability of sludge. For 4 g Fe(II)/kg TS and 60 g H₂O₂/kg TS, 19.4% higher methane production was achieved compared to raw sludge in biochemical methane potential assay. Fenton pre‐treatment resulted in the release of organic sludge components into the liquid phase. For 4 g Fe(II)/kg TS and 60 g H₂O₂/kg TS, dissolved organic carbon and total nitrogen in sludge's supernatant increased by 75.74 and 60.60%, respectively. Fenton pre‐treatment enhanced the filterability of sludge and it can be applied for conditioning purpose before mechanical dewatering units.     

Individual and Synergistic Effects of Metronidazole,Amoxicillin, and Ciprofloxacin on Methane Fermentation with Sewage Sludge

Methane fermentation is widely used to dispose of sewage sludge at wastewater treatment plants (WWTPs), due to production of renewable energy in the form of biogas. Antibiotics present in wastewater may accumulate in a sewage sludge. The aim of the present study is to investigate the impact of three antibiotics from different classes in three different doses on methane production from sewage sludge. For this purpose, metronidazole (MET), amoxicillin (AMO), and ciprofloxacin (CIP) are individually added to anaerobic reactors with sewage sludge collected from municipal WWTP. The antibiotics’ highest concentration (1024 mg kg^?1 of AMO; 512 mg kg^?1 of MET and CIP) lowers methane production and methane content in biogas. MET exerts the most marked effect and lowers methane production to 36.8 ± 3.7 mL CH₄ kg^?1 volatile solids. Tested antibiotics probably inhibit methanogenic archaea, which results in volatile fatty acids (VFAs) accumulation. Addition of MET results in accumulation of many kinds of VFAs with the highest concentration of acetic acid (17.52 ± 1.85 g L^?1). The addition of of AMO results in accumulation of butyric acid only (253.00 ± 15.89 g L^?1). However, addition of CIP results in accumulation of mainly acetic acid (7.58 ± 0.82 g L^?1) and isovaleric acid (2.01 ± 0.41 g L^?1). Next, synergistic effect of these antibiotics in a low concentration of 16 mg kg^?1 of AMO, 8 mg kg^?1 of MET, and 2 mg kg^?1 of CIP is measured in semi‐continuous conditions and causes inbibition of methane production and accumulation of VFAs.     

Effect of Saline Sludge on Anaerobic Digestion of Kitchen Waste for Methane Generation: Modeling and Fertilizer Recovery

A comparative study of methane recovery by co-digesting kitchen waste and saline sewage sludge is performed to evaluate its feasibility for waste minimization. The experiment is performed at 37 °C having a mixing speed of 100 rpm and pH of 6.49–7.5 in anaerobic mixed batch reactors. The higher salinity level of the saline sewage sludge reduces the degradation rate of kitchen waste causing an enhancement in soluble chemical oxygen demand by 133% compared with 280% when co-digesting with the non-saline sample. The inhibitory behavior is in line with the low volatile solid elimination efficiency of 31% of saline against 55% of non-saline sludge. The Gompertz modeling, based on the outcomes, fits the cumulative methane generation trends quite well, with a strong correlation coefficient (>0.994). Besides, use of the non-saline sludge results in three times more methane production than the saline sample digestion. Sludge recovery is 0.07 m³ sludge m⁻³ wastewater, and water recovery is 0.84 m³ m⁻³ wastewater. The liquid produced from the fermentation of the slurry can be used for irrigation as well as fertilization. Kitchen waste co-digestion with both sludge samples has been proven to be a practical method for exploiting the extra digestion capacity of wastewater treatment plants currently in operation, but it is more practical for non-saline sludge.     

Dimethylsulfoxidreduktase-Aktivität Charakterisierung der mikrobiellen Biomasseaktivität im Schlamm einer belüfteten Abwasserteichanlage

Dimethyl Sulfoxide Reduction Method for the Characterization of Biomass Activity in Sludge of an Aerated Lagoon The microbial biomass activity was studied in sludge from a wastewater lagoon (Hatzbachtal) which consisted of 4 aerated ponds and one polishing pond. The lagoon was characterized by low BOD₅ loading and high dilution because of water from the surroundings. Sludge samples were taken from 4 sampling sites of each aerated pond and from one site of the polishing pond. The biomass activity in the sludge samples was analysed with the help of dimethyl sulfoxide reductase (DRA) and dehydrogenase (DHA) activity. In addition, C_org-content was also determined. The effect of different reaction parameters on the DRA was studied in relation to incubation period, temperature and atmosphere as well as sludge weight and pH value. The results presented here show that a linear increase in the DRA occured for the sludge weight ranging from 0.1 to 0.5 g, incubation period from 0.5 to 11 h and incubation temperature from 20 to 50 °C. The pH spectrum from acidic to neutral did not effect the DMS formation in sludge. Although the values for DRA were always higher in anaerobic incubation of sludge than in aerobic incubation, the courses of the DRA in both conditions were parallel. Comparing the biomass activity in sludge from different sampling sites of the aerated ponds, the average C_org-content was found to be reflected by the DRA and DHA. Further, the variation in the DRA could represent also the influence of oxygen concentration. Therefore, a reduction in biomass activities indicated a decline in the availability of oxygen.     

Bestimmung geringer Wassergehalte in getrocknetem Klärschlamm mit Hilfe der Karl-Fischer-Titration

Determination of Low Water Contents in Dried Sludge with the Help of Karl Fischer Titration The accomplished investigations lead to the conclusion that direct water detection in sludge is impossible. This is due to the numerous possible reactants present. Even the extraction of the water by an inert solvent did not permit any realistic deductions. The water detection in sludge requires an external extraction. This may be realized by means of an additional extracting gas or the gaseous phase of the Karl Fischer reagent. The latter method was realized with the apparatus made by the company ECH Elektrochemie Halle. This alternative offers the benefit of avoiding a separate desiccation of the extracting gas. By means of a temperature gradient, the optimum heating conditions for the extraction of water from sludge may be determined. As there are only small quantities of water to be detected in the dried sludges, the best possible method seems to be microcoulometry.     

Kinetic Studies and Anaerobic Co‐digestion of Vegetable Market Waste and Sewage Sludge

The effect of anaerobic co‐digestion of vegetable market waste and sewage sludge was studied extensively. The effects of co‐digestion were compared with the separate digestion of vegetable market waste and sewage sludge. The batch studies were carried out using three bench scale reactors having 1.5 L working volume. The cumulative biogas production shows that the organic waste available from the vegetable waste contains easily biodegradable organic matter compared with the sewage sludge. First order reaction kinetics is maintained throughout the methanation fermentation. The reductions in volatile solids (VS) in the three reactors were in the range of 63–65 %. The specific gas production for vegetable waste was higher (0.75 L biogas/g VS_in and 1.17 L biogas/g VS_des) than for the sewage sludge (0.43 L biogas/g VS_in and 0.68 L biogas/g VS_des). Consequently, the specific gas production for the co‐digestion of the mixture of vegetable waste and sewage sludge (0.68 L biogas/g VS_in and 1.04 L biogas/g VS_des) was considerably higher than for the sewage sludge only. Batch kinetics of anaerobic digestion is useful in predicting the performance of digesters and for the design of appropriate digesters.     

Comparative Assessment of Sludge Pre‐Treatment Techniques to Enhance Sludge Dewaterability and Biogas Production

Effectiveness of ultrasonication, microwave technologies, and enzyme addition prior to anaerobic digestion is investigated using sludge samples taken from the secondary settling tank of a domestic wastewater treatment plant to improve methane production, enhance dewaterability characteristics of the sludge, and to reduce excess sludge. Microwave pre‐treatment (1500 W, 10 min at 175 °C) results in better extra digester performance (compared to the control reactor) in terms of methane production (25 m³ ton^?1 suspended solids (SS)) than ultrasound (no improvement) and enzyme pre‐treatment (11 m³ ton^?1 SS). While methane production is not improved as a result of ultrasonication pre‐treatment (15 000 kJ kg^?1 SS), a noticeable increase (19%) is observed in the case of microwave pre‐treatment. Higher compactibility values are obtained after ultrasonication and microwave application compared to the control (i.e., from 7.1 to 8.7 and 9.2%, respectively) before anaerobic digestion. Although ultrasonication and microwave application decrease the dewaterability of the raw sludge (capillary suction time (CST) from 827 to 1364 and 2290 s, respectively), similar dewaterability results are obtained at the end of the anaerobic digestion process for all pre‐treated sludge samples. An economic assessment of this study shows that pre‐treatment with microwave results in more than 10‐fold less net cost compared to the enzyme application.     

Enhancement of Biogas Generation by Addition of Lipase in the Co‐Digestion of Tannery Solid Wastes

Co‐digestion studies were carried out for biogas generation using fleshings as the primary substrate and a mixture of primary and secondary sludge generated during the treatment of tannery wastewater as the co‐substrate. Steapsin, a commercial grade lipase, was added to enhance the hydrolysis in anaerobic co‐digestion. The lipase dosages used were ranging between 0.25 and 1.0 g for a volatile solids input of 7.5 g. The performance of the co‐digestion was assessed from the volume of biogas generated. Experimental results revealed an optimum lipase dosage of about 0.75 g. At this dosage, the biogas generation was observed to increase by about 15% compared to that in the control without adding lipase. Further, the digestion with lipase addition was observed faster since the digestion period was reduced about 30%. This means that the capacity of the digester could also be reduced about 30% leading to savings in its installation cost.     

Kurzzeit-Toxizitätstests zur Messung der Toxizität von Chemikalien gegenüber Belebtschlamm

Short-term Toxicity Tests for the Measurement of Toxicity of Chemicals Towards Activated Sludge. To avoid severe damage to the activated sludge of a wastewater treatment plant it is necessary to control the sludge activity by means of biological test systems. Especially the short-term respiration assay and the dehydrogenase assay with resazurin as a redox-dye seem to be appropriate for this monitoring program. The practical performance of both test systems was optimized in some essential points. With the help of several reference substances both monitoring systems were tested for practical use as short-term toxicity tests. The results of the investigations showed that the inhibitory concentrations measured in both test systems were partially very different. In monitoring experiments with laboratory-scale wastewater treatment plants it could be shown that a positive correlation between respiration activity and dehydrogenase activity is not always given. Furthermore, a pH-dependent toxicity could be demonstrated for several substituted phenols.     

Treatment of Malting Wastewater in a Granular Sludge Sequencing Batch Reactor (SBR)

Aerobic granular sludge was successfully cultivated in a sequencing batch reactor (SBR) treating wastewater from the malting process with a high content of particulate organic matter. At an organic loading rate of 3.2 kg/(m³ d) COD_total and an influent particle concentration of 0.95 g/L MLSS an average removal of 50% in COD_total and 80% in COD_dissolved could be achieved. A comparison of granular and flocculent sludge grown under the same operating conditions showed no significant difference in removal efficiency although granules exhibited a higher metabolic activity in terms of specific oxygen uptake rate (r_{O2, X}). Two distinct mechanisms of particle removal were observed for granular sludge: during initial granule formation, particles were incorporated into the biofilm matrix. For mature granules, a high level of protozoa growth on the granule surface accounted for the ability to remove particulate COD. Combined evaluation of the development in MLSS content and sludge bed settling rate (i.e., mean derivative of the normalized sludge volume) was found to be an adequate method for monitoring the characteristic settling properties of a granulizing sludge bed. By means of this method, a distinct substrate gradient out of several operating conditions was concluded to have the biggest impact on the formation of aerobic granular sludge.     

Experiences with the Application of Starch Derivates in the Sludge Blanket Treatment

Sludge blanket clarifiers are nowadays quite commonly used in water treatment practice. In hydraulic aspect the sludge blanket represents essentially a fluidized layer of floc particles in water, in chemical-technological point of view it represents the orthokinetic stage of coagulation. In this work the authors examine the influence of hydraulic and technological factors on the sludge blanket operation. They examine also the possibility of improving the performance by the addition of organic flocculants, especially of starch derivates. They verify the results obtained from laboratory pilot-plant runs on a sludge blanket unit with the capacity of 100 I/sec. They conclude:

• a) The effects of local head losses and sludge blanket weight on the orthokinetic phase of coagulation are the same;
• b) the addition of organic flocculants will increase only slightly the mass density of the sludge blanket as well as that of a single floc;
• c) the separation efficiency of the sludge blanket will be improved with the increase of the Camp number;
• d) the starch derivates at a slightly higher dose than the commercial flocculants have the same effect as synthetic organic flocculants; however, the operation costs seem to be lower.

     

Modeling biogas emission at different methods of sewage sludge disposal

A methodological approach to the substantiation of a fire-safe approach to the disposal sewage sludge, ensuring minimal release of inflammable gases, is proposed. The criteria of biogas formation and dispersion in the sludge mass include the total amount, emission rate and dynamics have been derived from calculation models. They are used in alternative estimates of the advantages of different bunker designs and their filling rate.     

Response of soil aggregate disintegration to the different content of organic carbon and its fractions during splash erosion

Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m⁻² mm⁻¹ and 12 m⁻² mm⁻¹. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.     

Simulation experiments on gas production from hydrate-bearing sediments

Experiments were made on 58 sediment samples from four sites(1244,1245,1250 and 1251) of ODP204 at five temperature points(25,35,45,55 and 65℃) to simulate methane production from hydrate-bearing sediments.Simulation results from site 1244 show that the gas components consist mainly of methane and carbon dioxide,and heavy hydrocarbons more than C2+ cannot be detected.This site also gives results,similar to those from the other three,that the methane production is controlled by experimental temperatures,gene...     

Laboratory Testing of Sulfamethoxazole and its Metabolite Acetyl‐Sulfamethoxazole in Soil

The fate of ¹⁴C‐labeled sulfamethoxazole and acetyl‐sulfamethoxazole in soil has been investigated with special respect to possible entry routes of human and veterinary pharmaceuticals into soil environments. Therefore, the stability of the test substances was monitored first in sewage sludge and bovine manure. Within the incubation period of 72 d, 1% at maximum of the initially applied radiotracers was released as ¹⁴C‐carbon dioxide while ?75% was transferred to non‐extractable residues that were operationally defined by the ethyl acetate extraction. Test‐sludge and test‐manure samples with defined aged residues were prepared and, supplementary to standard solutions, applied to silty‐clay soil samples. After standard and test‐sludge application, soil/water distribution coefficients of K_d < 5 L kg^–1 were determined revealing both test substances as potential leachers. In contrast, the sorption of sulfamethoxazole increased after test‐manure application (K_d > 10 L kg^–1). In the long‐term degradability tests, the metabolic fate of both test substances was characterized by the continuous decrease of extractable residues, resulting in disappearance times of DT₉₀ ? 33 d, and the increase of non‐extractable residues. Mineralization reached 11% at maximum. Thereby, the dynamics of these processes differed whether the test substances were applied via standard, test‐sludge or test‐manure application. This fact emphasized the relevance of entry route specific matrix effects on the fate of both test substances in soil.     

Fate of Benzalkonium Chloride in a Sewage Sludge Low Temperature Conversion Process Investigated by LC‐LC/ESI‐MS/MS

Thermocatalytic low temperature conversion (LTC) is a new method for the disposal of sewage sludge. Using this method, sludge is converted into a residual solid (coal) along with reaction water, oil, and non‐condensable gases. The oil can be used as an energy source and the coal as a substitute for charcoal. To this end, it is important to determine whether there are any easily available contaminants present in the coal generated by the process. Contaminants that can be strongly sorbed by sewage sludge solids are, e. g., pharmaceuticals and disinfectants. As an example the fate of the persistent and strong adsorbing disinfectant benzalkonium chloride (BAC) has been investigated within the LTC process. The sewage sludge was spiked with BAC and then subjected to the LTC process. The resulting coal was extracted and analyzed using LC‐LC/ESI‐MS/MS (ion trap). BAC could not be detected in the LTC coal, although it could be extracted from the spiked sludge before the LTC treatment. It can thus be concluded that the investigated compound is not easily available in the coal, and hence that its use does not present a risk.     

Vergleich ausgewählter Elutionsverfahren zur Beurteilung der Mobilität von Metallen

Comparison of Selected Elution Procedures for the Valuation of the Mobility of Metals from Sediment and Sewage Sludge Several methods of extraction are generally used to evaluate environmental or ecological toxicity and deposition of waste material. In this paper, the application of the German standard methods DIN 38414-S7, DIN 38414-S4, pH_stat method, “Schweizer method” (elution test, Switzerland), and some variants of the pH_stat method on two very different samples are described. A rudimental sediment and a municipal sewage sludge are chosen as sample materials. The metal contents of extract solutions are determined by ICP-OES. The results of the DIN-S4 extractions depend definitely on the mechanic way of movement, i.e. the amount of heavy metals which are mobilized out of the samples differs considerably. In fact, DIN-S7 in combination with DIN-S4 is not sufficient to estimate the mobility of heavy metals. Solid samples should only be evaluated by applying a combination of several methods of extraction. The usefulness of the pH_stat method for an evaluation is discussed.     

Biogas charging and dissipating process and its accumulation in the Sebei gasfield,Qaidam Basin,China

The Sebei gasfield is the largest biogas accumulation found in China and many reservoirs and seal rocks superposed on a syndepositional anticline in Quaternary.The biogas charging and dissipating process and its distribution have been a research focus for many years.The authors suggest a diffusing and accumulating model for the biogas,as they find that the shallower the gas producer,the more methane in the biogas,and the lighter stable carbon isotope composition of methane.Based on the diffusing model,diffused biogas is quantitatively estimated for each potential sandy reservoir in the gasfield,and the gas charging quantity for the sandy reservoir is also calculated by the diffused gas quantity plus gas reserve in-place.A ratio of diffusing quantity to charging quantity is postulated to describe biogas accumulating state in a sandy reservoir,if the ratio is less than 0.6,the reservoir forms a good gas-pool and high-production layer in the gasfield,which often occurs in the reservoirs deeper than 900 m;if the ratio is greater than 0.6,a few gas accumulated in the reservoir,which frequently exists in the reservoirs shallower than 900 m.Therefore,a biogas accumulation model is built up as lateral direct charging from gas source for the sands deeper than 900 m and indirect charging from lower gas-bearing sands by diffusion at depth shallower than 900 m.With this charging and diffusion quantitative model,the authors conducted re-evaluation on each wildcat in the central area of the Qaidam Basin,and found many commercial biogas layers.