scholarly journals Mathematical modelling of waste activated sludge thermal disintegration

2018 ◽  
Vol 23 ◽  
pp. 00027
Author(s):  
Sylwia Myszograj ◽  
Magdalena Wojciech

Chemical Oxygen Demand (COD) solubilisation was used to evaluate the impact of thermal pretreatment on the transfer of sewage sludge from particulate to soluble phase. It was gathering the experimental data needed for building of empirical mathematical model describing the relation between applied temperature and time and rate of COD solubilisation and degradation. In view of repeated measurements, in order to describe the relationship between changes in the fraction of dissolved COD and the time and temperature, mixed models have been adopted where by fixed factor measurement conditions have been adopted: time and temperature, while the random factor changes the characteristics of waste activated sludge. Linear and logistic nonlinear mixed models were analyzed. The tests demonstrated that all variables are statistically significant in assessing their impact on the efficiency of liquefaction of sludge. On the basis of the estimated model, the temperature rise of 10°C increases degree of disintegration 1.7% above the average treatment time for 0.5h, by 2.6% for 1 hour, and by 3.9% for 2h. COD values decrease between 3 to 23% at temperatures in the range of 55 to 115°C. At higher temperatures COD was reduced in the range of 32 to 44%. Disintegration time did not have the significant impact on the degradation effect.

2018 ◽  
Vol 78 (8) ◽  
pp. 1772-1781 ◽  
Author(s):  
Hyungjun (Brian) Jo ◽  
Wayne Parker ◽  
Peiman Kianmehr

Abstract A range of thermal pretreatment conditions were used to evaluate the impact of high pressure thermal hydrolysis on the biodegradability of waste activated sludge (WAS) under aerobic and anaerobic conditions. It was found that pretreatment did not increase the overall extent to which WAS could be aerobically biodegraded. Thermal pretreatment transformed the biodegradable fraction of WAS (XH) to readily biodegradable chemical oxygen demand (COD) (SB) (16.5–34.6%) and slowly biodegradable COD (XB) (45.8–63.6%). The impact of pretreatment temperature and duration on WAS COD fractionation did not follow a consistent pattern as changes in COD solubilization did not correspond to the observed generation of SB through pretreatment. The pretreated WAS (PWAS) COD fractionations determined from aerobic respirometry were employed in anaerobic modeling and it was concluded that the aerobic and anaerobic biodegradability of PWAS differed. It was found that thermal pretreatment resulted in as much as 50% of the endogenous decay products becoming biodegradable in anaerobic digestion. Overall, it was concluded that the COD fractionation that was developed based upon the aerobic respirometry was valid. However, it was necessary to implement a first-order decay process that reflected changes in the anaerobic biodegradability of the endogenous products through pretreatment.


2013 ◽  
Vol 67 (12) ◽  
pp. 2827-2831 ◽  
Author(s):  
W. Charles ◽  
B. Ng ◽  
R. Cord-Ruwisch ◽  
L. Cheng ◽  
G. Ho ◽  
...  

Anaerobic digestion of waste activated sludge (WAS) is relatively poor due to hydrolysis limitations. Acid and alkaline pretreatments are effective in enhancing hydrolysis leading to higher methane yields. However, chemical costs often prohibit full-scale application. In this study, 12 V two-chamber electrolysis using an anion exchange membrane alters sludge pH without chemical dosing. pH dropped from 6.9 to 2.5 in the anode chamber and increased to 10.1 in the cathode chamber within 15 h. The volatile suspended solids solubilisation of WAS was 31.1% in the anode chamber and 34.0% in the cathode chamber. As a result, dissolved chemical oxygen demand increased from 164 to 1,787 mg/L and 1,256 mg/L in the anode and cathode chambers, respectively. Remixing of sludge from the two chambers brought the pH back to 6.5, hence no chemical neutralisation was required prior to anaerobic digestion. Methane yield during anaerobic digestion at 20 d retention time was 31% higher than that of untreated sludge. An energy balance assessment indicated that the non-optimised process could approximately recover the energy (electricity) expended in the electrolysis process. With suitable optimisation of treatment time and voltages, significant energy savings would be expected in addition to the benefit of decreased sludge volume.


Author(s):  
Basak Savun ◽  
Uwe Neis ◽  
Nilsun H. Ince ◽  
Orhan Yenigün

AbstractThe key point of waste activated sludge (WAS) pretreatment is to rupture the cell wall for allowing the release of intracellular matter that acts as a bioavailable substrate in anaerobic digestion processes. In this regard, ultrasonic irradiation has been one of the most effective tools owing to the unique properties of ultrasound to produce extreme conditions in heterogeneous liquids such as waste activated sludge. The present study investigates the impact of short-frequency ultrasound on disintegration, biodegradability and dewatering characteristics of sewage sludge by monitoring soluble chemical oxygen demand (sCOD), dissolved organic carbon (DOC), soluble proteins, total dissolved nitrogen, particle size and dewaterability of raw and sonicated sludge samples to optimize the operating parameters. The results showed that short wave ultrasound is a highly effective method of WAS treatment, because it provides high degrees of disintegration and biomass transfer from sludge solids to the aqueous phase, thus resulting in enhanced biodegradability.


2014 ◽  
Vol 70 (2) ◽  
pp. 200-208 ◽  
Author(s):  
Chunxue Yang ◽  
Aijuan Zhou ◽  
Yanan Hou ◽  
Xu Zhang ◽  
Zechong Guo ◽  
...  

Hydrolysis is known as the rate-limiting step during waste activated sludge (WAS) digestion. The optimization of the culture conditions of Geobacillus sp. G1 for enhancing WAS hydrolysis was conducted in this study with uniform design and response surface methodology. Taking the lysis rate of Escherichia coli as the response, the Plackett–Burman design was used to screen the most important variables. Experimental results showed that the maximum predicted lysis rate of E. coli was 50.9% for 4 h treatment time with concentrations of skim milk, NaCl and NH4SO4 at 10.78, 4.36 and 11.28 g/L, respectively. The optimized dosage ratio of Geobacillus sp. G1 to WAS was 35%:65% (VG1:VWAS). Under this condition, soluble protein was increased to 695 mg chemical oxygen demand (COD)/L, which was 5.0 times higher than that obtained in the control (140 mg COD/L). The corresponding protease activity reached 1.1 Eu/mL. Scanning electron microscopy showed that abundant cells were apparently lysed with treatment of Geobacillus sp. G1.


2021 ◽  
Vol 36 (Supplement_1) ◽  
Author(s):  
J Devroe ◽  
K Peeraer ◽  
T D’Hooghe ◽  
J Boivin ◽  
J Vriens ◽  
...  

Abstract Study question What is the impact of providing couples with their IVF-prognosis on expectations and anxiety in women and men on the day of embryo transfer? Summary answer Only couples with a less than average IVF-prognosis updated their high expectations and IVF-prognosis was negatively associated with anxiety, especially in women. What is known already Female IVF-patients are known to expect a pregnancy rate per IVF-cycle of no less than 49-55%. Qualitative interviews and a survey showed that well informed women expect unrealistically high pregnancy rates as they think that their (family’s) fertility and their clinic is better than average. Several prognostic models have recently been published. The adapted van Loendersloot model including clinical and laboratory characteristics proved performant for our clinic (AUC=0.74) and was validated internally (Devroe et al, BMJ Open, 2020). The impact of providing couples with their IVF-prognosis on expectations and wellbeing of female and male patients has yet to be studied. Study design, size, duration A prospective survey, questioning a final sample of 148 partnered individuals, completing their 2nd-6th IVF-cycle (2019-2020) in a University clinic, on the days of oocyte aspiration (OA) and fresh embryo transfer (ET). Thirty other partnered individuals declined participation (participation rate=85%) and 26 were excluded due to ET-cancellation. The IVF-prognosis (live birth rate, LBR, per completed IVF-cycle including fresh and frozen ETs from the same ovarian stimulation) was calculated with the adapted van Loendersloot model. Participants/materials, setting, methods Each partner reported their perception of their expected IVF-LBR on a visual analogue scale on the day OA. After being informed on their IVF-prognosis by gynaecologists, they re-rated their expected IVF-LBR and filled out the reliable ‘STAI-State-Anxiety Inventory’ on the day of fresh ET. Linear mixed models, taking account of partnering and assessing the association with gender, explored whether individuals updated their expected IVF-LBR after receiving their IVF-prognosis and whether IVF-prognosis and anxiety were associated. Main results and the role of chance The mean IVF-prognosis was 30.9% (±16.8). The 148 partnered individuals had a mean expected IVF-LBR of 59.1% (±20.0) on the day of OA (no gender effect; p = 0.079). After being informed on their IVF-prognosis (day of ET), women’s and men’s mean expected IVF-LBR was 50.9% (±24.5) and 58.1% (±22.1), respectively (gender effect; p = 0.002). Linear mixed models, including couple and time as random factors, did not show an effect of time on expected IVF-LBRs (p = 0.15). Although women were more likely than men to update their expected IVF-LBR (p = 0.002), the updates were not significantly different from the IVF-LBR expected on the day of OA (p = 0.10). Women were more anxious than men (41.5±10.6 and 21.9±7.2, respectively, p < 0.001) after being given their IVF-prognosis. Linear mixed models, including couple as a random factor, showed an association between IVF-prognosis and anxiety (p = 0.016), especially in women (gender effect; p = 0.004). Subgroup analysis showed that partnered individuals with lower than average prognoses (n = 78) did update their expected IVF-LBR (p = 0.036) while others (n = 70) did not update their expected IVF-LBR (p = 0.761). Among the subgroup with lower prognoses women were more likely to update their expected IVF-LBR than men (p = 0.013), while no gender effect was observed among the subgroup with higher IVF-prognoses (p = 0.078). Limitations, reasons for caution This is an explorative study in preparation of an adequately powered randomized controlled trial, testing whether couples who are informed on their IVF-prognosis update their expected IVF-LBR and whether this causes anxiety, as compared to care as usual in which couples are not informed on their IVF-prognosis. Wider implications of the findings Men and especially women with a less than average prognosis update their IVF-expectations after having received this prognosis which may trigger anxious reactions. These findings should be re-examined in an RCT. Following up the effect of sharing IVF-prognoses on longer-term distress and IVF-discontinuation would be interesting. Trial registration number not applicable


2013 ◽  
Vol 69 (2) ◽  
pp. 269-277 ◽  
Author(s):  
C. Da Ros ◽  
C. Cavinato ◽  
F. Cecchi ◽  
D. Bolzonella

In this study the anaerobic co-digestion of wine lees together with waste activated sludge in mesophilic and thermophilic conditions was tested at pilot scale. Three organic loading rates (OLRs 2.8, 3.3 and 4.5 kgCOD/m3d) and hydraulic retention times (HRTs 21, 19 and 16 days) were applied to the reactors, in order to evaluate the best operational conditions for the maximization of the biogas yields. The addition of lee to sludge determined a higher biogas production: the best yield obtained was 0.40 Nm3biogas/kgCODfed. Because of the high presence of soluble chemical oxygen demand (COD) and polyphenols in wine lees, the best results in terms of yields and process stability were obtained when applying the lowest of the three organic loading rates tested together with mesophilic conditions.


1996 ◽  
Vol 34 (10) ◽  
pp. 43-50 ◽  
Author(s):  
Oliver J. Hao ◽  
Shin Chien-Jen ◽  
Lin Cheng-Fang ◽  
Jeng Fu-Tien ◽  
Chen Zen-Chyuan

Conventional parameters such as chemical oxygen demand and suspended solids may not detect toxic compounds present in a variety of industrial wastewaters and treated wastes. Thus, the presence of toxicity in many industrial wastes presents a significant impact on biological wastewater treatment, and exerts adverse effects on receiving waters. Because of their easy technique and rapid turnaround results, the Microtox tests were used in this study to pinpoint unusual wastewaters, evaluate the toxicity reduction through activated sludge processes, observe the impact of excessive chemical addition to meet the transparency standard, and measure the impact of waste discharge on one particular receiving water. It was found that the results of Microtox tests were useful for such purposes; i.e., low COD wastes exhibited high Microtox toxicity; some activated sludge processes removed significant toxicity; and some effluents from coagulation/oxidation processes showed an increased toxicity. The application of the Microtox test to wastewater management is discussed.


Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2657
Author(s):  
Elwira Nowobilska-Majewska ◽  
Piotr Bugajski

The aim of this study was to determine the condition of activated sludge in the biologic reactor located in the collective wastewater treatment plant in Nowy Targ (Poland) based on OUR tests in the aspect of the impact of sludge’s concentration in the biologic reactor and dependence of BOD5/TN and BOD5/TP in wastewater flowing into the biologic reactor. The analysis was conducted based on test results from 61 samples of activated sludge taken from the biologic reactor and 61 samples of wastewater flowing into the biologic reactor. The analysis included the concentration of sludge in the biologic reactor. The following indicators were analyzed in wastewater flowing into the reactor: biochemical oxygen demand (BOD5), total nitrogen (TN) and total phosphorus (TP). The statistical analysis concerning the impact of the analyzed factors on oxygen uptake rate (OUR) tests was developed based on the Pearson’s correlation coefficient and partial correlation of many variables. Based on the results of the partial correlation analysis, nomograms were developed to determine the condition of activated sludge microorganisms (OUR) based on the BOD5/TN and BOD5/TP connection and knowledge of the sludge concentration in the bioreactor of the treatment plant. The presented nomograms can be formulated for each bioreactor based on activated sludge technology related the load of organic and biogenic pollutants in the wastewater flowing into the bioreactor and the concentration of the sludge in the bioreactor.


Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1580
Author(s):  
Farokh laqa Kakar ◽  
Ahmed El Sayed ◽  
Neha Purohit ◽  
Elsayed Elbeshbishy

The main objective of this study was to evaluate the hydrothermal pretreatment’s retention time influence on the volatile fatty acids and biomethane production from thickened waste activated sludge under mesophilic conditions. Six different retention times of 10, 20, 30, 40, 50, and 60 min were investigated while the hydrothermal pretreatment temperature was kept at 170 °C. The results showed that the chemical oxygen demand (COD) solubilization increased by increasing the hydrothermal pretreatment retention time up to 30 min and stabilized afterwards. The highest COD solubilization of 48% was observed for the sample pretreated at 170 °C for 30 min. Similarly, the sample pretreated at 170 °C for 30 min demonstrated the highest volatile fatty acids yield of 14.5 g COD/Lsubstrate added and a methane yield of 225 mL CH4/g TCODadded compared to 4.3 g COD/Lsubstrate added and 163 mL CH4/g TCODadded for the raw sample, respectively. The outcome of this study revealed that the optimum conditions for solubilization are not necessarily associated with the best fermentation and/or digestion performance.


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