Novel anaerobic digestion process with sludge ozonation for economically feasible power production from biogas

A novel process scheme was developed to achieve economically feasible energy recovery from anaerobic digestion. The new process scheme employs a hybrid configuration of mesophilic and thermophilic anaerobic digestion with sludge ozonation: the ozonated sludge is first degraded in a thermophilic digester and then further degraded in a mesophilic digester. In small-scale pilot experiments of the new process scheme, degradation of VSS improved by 3.5% over the control (mesophilic-only configuration) with 20% less ozone consumption. Moreover, biogas conversion also improved by 7.1% over the control. Selective enrichment of inorganic compounds during centrifugation produced a dewatered sludge cake with very low water content (59.4%). This low water content in the sludge cake improved its auto-thermal combustion potential during incineration and added to the overall energy savings. We conducted a case study to evaluate power generation from biogas for a municipal wastewater treatment plant with an average dry weather flow of 43,000 m3/d. Electricity production cost was 5.2 ¢/kWh for the advanced process with power generation, which is lower than the current market price of 7.2 ¢/kWh. The new anaerobic digestion scheme with power generation may reduce greenhouse gas emissions by about 1,000 t-CO(2)/year compared with the conventional process without power generation.

Upgrading of the anaerobic digestion of waste activated sludge by combining temperature-phased anaerobic digestion and intermediate ozonation

Upgrading of the anaerobic digestion of waste activated sludge (WAS) by the combination of temperature-phased two-stage digestion and intermediate ozonation was investigated by a continuous experiment with two processes, TM and TOM. The TM process is a temperature-phased two-stage system, which consists of a thermophilic digester and a mesophilic digester in series. The TOM process is a temperature-phased two-stage process with the intermediate ozonation. Two processes were operated at hydraulic retention times of 30 days for over 123 days. Waste activated sludge taken from wastewater treatment plant was fed as a substrate. Microbial community structure in each digester was analysed with molecular tools. Despite of less amount of ozone dose in TOM than ozone pre-treatment process, better effect of ozonation on performance improvement was obtained in TOM. TOM had the highest methane yield and COD(Cr) reduction among comparative processes. Furthermore, flocculation efficiency of TOM followed that of mesophilic digestion. Quality of dewatered supernatant is comparable to mesophilic digestion.

Evaluation of state variable interface between the Activated Sludge Models and Anaerobic Digestion Model no 1

For plant wide modelling of wastewater treatment, it is necessary to develop a suitable state variables interface for integrating state of the art models of ASM and ADM1. ADM1 currently describes such an interface, however, its suitability needs to be experimentally evaluated. In this study, we characterised activated sludge under aerobic and anaerobic conditions to obtain representative state variables for both models. ASM state variables of X(S), X(H) and X(I) (as obtained from aerobic tests) and ADM1 state variables of X(C) and X(I) (as obtained from anaerobic tests) were then correlated to assess the suitability of current interface. Based on the seven datasets of this study and seven datasets from literatures, it was found that in general ASM state variables were well correlated to the state variables of ADM1. The ADM1 state variable of X(C) could be correlated to the sum of state variables of X(S) and X(H), while X(I) in both the models showed direct correspondence. It was also observed that the degradation kinetics of X(C) under anaerobic condition could be better described by individual degradation kinetics of X(S) and X(H). Therefore, to establish a one to one correspondence between ASM and ADM1 state variables and better description of degradation kinetics in ADM1, replacing the composite variable of X(C) by the state variables of X(S) and X(H) is recommended.

Modified ADM1 structure for modelling municipal primary sludge hydrolysis

This study elaborates the rate-limiting steps of particle disintegration/hydrolysis of primary sludge using methane production rate (MPR) curves from multiple batch experiments. Anaerobic batch degradation of fresh primary sludge showed a complex MPR curve marked with two well-defined temporal peaks. The first immediate peak was associated with the degradation of relatively readily hydrolysable substrates, while the second delayed peak was associated with the degradation of large-sized particles. For simulating the second delayed peak, it was necessary to consider a more elaborate particle disintegration/hydrolysis model. Based on the anaerobic respirograms of 17 runs in four datasets and using a substrate characterisation approach similar to activated sludge models (ASMs), the primary sludge was classified into three biodegradable fractions having different kinetics. These are (1) a hydrolysable substrate (X(Settle-I)) showing a degradation typical to slowly biodegradable compounds, (2) a substrate fraction (X(Settle-II)) having a degradation similar to lysis of biomass fraction and (3) a substrate requiring disintegration before hydrolysis (X(Settle-III)) representing the large-sized particles in primary sludge. Based on these results, modifications in the model structure of anaerobic digestion model no. 1 (ADM1) are proposed to improve the modelling of primary sludge solid degradation in anaerobic digesters.

An approach for substrate mapping between ASM and ADM1 for sludge digestion

Kinetic modelling of the hydrolysis stage of municipal activated sludge, which is presumed to be the rate-limiting step in the anaerobic sludge digestion process, was studied by measuring methane production rate (MPR) in anaerobic batch tests. The MPR curves revealed that the degradable organic components in municipal sludge could be classified into two fractions having different kinetics. The first fraction (XS1) constituted about 55% of the sludge COD and degraded with first-order kinetics. The second fraction (XS2), which degraded during the initial phase, accounted for about 21% of sludge COD. The degradation kinetics for XS2 was expressed by Contois-type equation with respect to concentration of substrate in the fed sludge and that of active biomass in the mixture. Simultaneous batch aerobic respirometric tests showed that the activated sludge was composed of 53% heterotrophic biomass (XH-Aerobe) COD and 20% of slowly biodegradable COD (XS), that had same kinetic expressions as observed in the batch anaerobic tests. The observed correlation between substrate fractions suggests XS1 and XS2 could be directly mapped to the aerobic state variables of XH-Aerobe and Xs respectively. The degradation of XS1 seems to be anaerobic decay of XH-Aerobe while XS2 is thought to be hydrolysis of XS by microcosm of the sludge.

Anaerobic digestion with partial ozonation minimises greenhouse gas emission from sludge treatment and disposal

A novel anaerobic digestion process combined with partial ozonation on digested sludge was demonstrated for improving sludge digestion and biogas recovery by full-scale testing for 2 years and its performance was compared with a simultaneously operated conventional anaerobic digestion process. The novel process requires two essential modifications, which are ozonation for enhancing the biological degradability of sludge organics and concentrating of solids in the digester through a solid/liquid separation for extension of SRT. These modifications resulted in high VSS degradation efficiency of ca. 88%, as much as 1.3 times of methane production and more than 70% reduction in dewatered sludge cake production. Based on the performance, its energy demands and contribution for minimisation of greenhouse gas emission was evaluated throughout an entire study of sludge treatment and disposal schemes in a municipality for 130,000 p.e. The analysis indicated that the novel process with power generation from biogas would lead to minimal greenhouse gas emission because the extra energy production from the scheme was expected to cover all of the energy demand for the plant operation, and the remarkable reduction in dewatered sludge cake volumes makes it possible to reduce N2O discharge and consumption of fossil fuel in the subsequent sludge incineration processes.

Continuous hydrogen production from organic waste

The antibiotic effects of lactic acid bacteria, Lactobacillus paracasei, on hydrogen production were investigated using glucose as the substrate for the batch experiments. The effects of lactic acid bacteria on hydrogen fermentation depended on pH and the inhibition of hydrogen-producing bacteria was prevented by keeping the pH over 5.0. Then, a continuous hydrogen production experiment was conducted by using bean curd manufacturing waste as an actual organic waste at pH 5.5 at 35 degrees C. The increase of the substrate concentration and the addition of nitrogen gave precedence to acetic and butyric acids production in the metabolic pathway and suppressed propionic acid production. As the result, continuous hydrogen production from municipal organic waste was enabled.

Full-scale application of anaerobic digestion process with partial ozonation of digested sludge

For improving sludge digestion and biogas recovery, a new anaerobic digestion process combined with ozonation was tested at a full-scale unit for 2 years and its performance was compared with a simultaneously operated conventional anaerobic digestion process. The new process requires two essential modifications, which includes ozonation for enhancing the biological degradability of sludge organics and concentrating of solids in the digester through a solid/liquid separation for extension of SRT. These modifications resulted in high VSS degradation efficiency of ca. 88%, as much as 1.3 times of methane production and more than 70% reduction in dewatered sludge cake production. Owing to accumulation of inorganic solids in the digested sludge, water content of the dewatered sludge cake also reduced from 80% to 68%. An energy analysis suggested that no supplemental fuel was necessary for the subsequent incineration of the cake from the new process scheme. The process is suitable to apply to a low-loaded anaerobic digestion tank, where power production is used.

Development of a new type of anaerobic digestion process equipped with the function of nitrogen removal

In order to develop a new type of anaerobic digestion process equipped with a nitrogen removal function, denitrification of nitrate nitrogen (NO3-N) in anaerobic acidogenesis of organic fraction of municipal waste (OFMSW) was investigated by two semi-continuous reactors. Reactor 1 and Reactor 2 were fed by 3% and 7% of solids concentration of synthetic garbage, respectively. Generation of nitrogen gas (N2) and ammonium nitrogen (NH4-N) was simultaneously observed in the low load of nitrate (NO3-N) (below 0.68 g NO3-N/L). In Reactor 1, ammonium nitrogen generation decreased as the addition of nitrate increased. Finally, the increase of the addition of nitrate resulted in the increase of acetic acid production.

Optimal process configuration for anaerobic digestion with ozonation

Economical source minimization of excess sludge production is an attractive option to deal with the problem of sludge disposal under strict disposal standards. In this paper long-term operational results for two different process configurations that combine oxidative ozone treatment with anaerobic sludge digestion are described. In the first configuration ozone pretreatment was combined with chemostat anaerobic digestion while in the second configuration ozone pre/post-treatments were combined with an anaerobic digester operated without solid removal. From the results of chemostat experiments, the ozone pretreatment solubilized around 19% and 37% of the solids at 0.015 and 0.05 gO3/gTS ozone dose respectively. The ozone pretreatment resulted in improved TVS reduction efficiencies and the degradation efficiencies were observed to depend on the applied ozone dose and system SRT. The TVS degradation efficiency for pre-ozonated sludge at an ozone dose of 0.05 gO3/gTS was 59% as compared to 31% for the control reactor fed with un-ozonated sludge. Test results with the second configuration indicated that overall TVS removal efficiencies for a process scheme with post-ozonation could be improved up to 85% with a minimum ozone dose of 0.045 gO3/gTVS-fed. However, since no solids (except that for sampling) were withdrawn in this configuration, the accumulated total solids in the reactors increased to 28 g/l to 30 g/l at pseudosteady state. The average specific methane recoveries were observed to be 0.36 lCH4/gTVS fed which were slightly lower than theoretically expected. Based on the experimental results, important points in the choice of process configuration are discussed.

Alkaline subcritical-water treatment and alkaline heat treatment for the increase in biodegradability of newsprint waste

This work describes two alkaline semicontinuous processes for the conversion of refractory organic materials into biodegradable substances. Newsprint was used as a lignocellulosic waste. Methane conversion efficiencies and cellulose removals were investigated for the two following processes: alkaline subcritical-water treatment (ASWT) coupled with methane fermentation and alkaline heat treatment (newsprint heated with steam in an autoclave; AHT) coupled with methane fermentation with a neutral subcritical-water treatment (NSWT) recycle. Results showed that for ASWT coupled with methane fermentation higher methane conversion efficiencies and higher cellulose removals were achieved as HRT increased. At HRT = 20 days, average CH4 conversion efficiency and average cellulose removal reached 26% and 44%, respectively. After a final HRT of 40 days, average CH4 conversion efficiency and average cellulose removal reached 50% and 60%, respectively. On the other hand, for AHT coupled with methane fermentation, methane conversion efficiencies did not show a greater improvement using this pretreatment process. Average conversion reached 9% with an average cellulose removal of 20%. In order to improve the yield of the reactor, approximately one-third of the effluent was recycled using NSWT (150 degrees C; neutral pH). Methane conversion efficiency of this process increased as more recycles were performed. For the fifth operation, the total average methane conversion efficiency was 44% with a total average cellulose removal of 55%.

Effect of iron concentration on hydrogen fermentation

The effect of the iron concentration in the external environment on hydrogen production was studied using sucrose solution and the mixed microorganisms from a soybean-meal silo. The iron concentration ranged from 0 to 4,000 mg FeCl2 l(-1). The temperature was maintained at 37 degrees C. The maximum specific hydrogen production rate was found to be 24.0 ml g(-1) VSS h(-1) at 4,000 mg FeCl2 l(-1). The specific production rate of butyrate increased with increasing iron concentration from 0 to 20 mg FeCl2 l(-1) and decreased with increasing iron concentration from 20 to 4,000 mg FeCl2 l(-1). The maximum specific production rates of ethanol (682 mg g(-1) VSS h(-1)) and butanol (47.0 mg g(-1) VSS h(-1)) were obtained at iron concentrations of 5 and 3 mg FeCl2 l(-1), respectively. The maximum hydrogen production yield of 131.9 ml g(-1) sucrose was obtained at the iron concentration of 800 mg FeCl2 l(-1). The maximum yields of acetate (389.3 mg g(-1) sucrose), propionate (37.8 mg g(-1) sucrose), and butyrate (196.5 mg g(-1) sucros) were obtained at iron concentrations of 3, 200 and 200 mg FeCl2 l(-1), respectively. The sucrose degradation efficiencies were close to 1.0 when iron concentrations were between 200 and 800 mg FeCl2 l(-1). The maximum biomass production yield was 0.283 g VSS g(-1) sucrose at an iron concentration of 3,000 mg FeCl2 l(-1).

Relationship between doubling time of liver metastases from colorectal carcinoma and residual primary cancer

BACKGROUND

The doubling times of liver metastases were calculated in order to clarify their usefulness in predicting the presence of residual cancer in the abdominal cavity in patients who had undergone curative resection of primary colorectal cancer.

PATIENTS AND METHODS

Tumor doubling times were calculated retrospectively in 22 patients by serial measurement of the size of their liver metastases.

RESULTS

Patients with a tumor doubling time of less than 92.4 days had a significantly poorer prognosis than those with a doubling time more than or equal to 92.4 days (p < 0.05). Local recurrence or peritoneal dissemination was significantly more likely to occur when the tumor doubling time was less than 92.4 days than when it was more than or equal to 92.4 days (p < 0.01).

CONCLUSION

The doubling time of hepatic metastases in patients with colorectal carcinoma may be a useful prognostic indicator, with patients who have a shorter tumor doubling time carrying a greater risk of residual primary cancer in the abdominal cavity.

Biological hydrogen potential of materials characteristic of the organic fraction of municipal solid wastes

The purpose of this study is to investigate the biological hydrogen production potential of individual organic fraction of municipal solid wastes (OFMSW) by batch experiments. Seven varieties of typical organic solid wastes including rice, cabbage, carrot, egg, lean meat, fat and chicken skin were selected to estimate the hydrogen production potential. Among the OFMSW, carbohydrate produced the most hydrogen through biological hydrogen fermentation compared with proteins or lipids. Subsequently, the biological hydrogen production potentials of some individual carbohydrate were measured: cabbage, 26.3-61.7 mL/g-VS; carrot, 44.9-70.7 mL/g-VS; and rice, 19.3-96.0 mL/g-VS. The hydrogen percentages of the total biogas produced from cabbage, carrot and rice were 33.9-55.1%, 27.7-46.8% and 44.0-45.6%, respectively.

Effect of moisture content on anaerobic digestion of dewatered sludge: ammonia inhibition to carbohydrate removal and methane production

The purpose of this study is to investigate the effect of moisture content on anaerobic digestion of dewatered sewage sludge under mesophilic condition. The moisture contents of sludge fed to reactors were 97.0%, 94.6%, 92.9%, 91.1% and 89.0%. The VS removal efficiency changed from 45.6% to 33.8%, as the moisture content of sludge fed to digester decreased from 97.0% to 89.0%. The carbohydrate removal efficiency also decreased from 71.1% to 27.8%. Methane production decreased when the moisture content of sludge was lower than 91.1%. The number of glucose consuming acidogenic bacteria was decreased from 3.1 x 10(6) to 3.1 x 10(8) (MPN/mL) as the moisture content decreased from 91.1% to 89.0%. The numbers of hydrogenotrophic and acetoclastic methanogenic bacteria decreased by one order of magnitude when the moisture content was lower than 91.1%. The decrease in numbers of glucose consuming acidogenic bacteria and methanogenic bacteria was found to correspond to the decrease in the carbohydrate removal efficiency and the accumulation of propionic acid. Batch experiments showed that acetoclastic methanogenic bacteria were acclimated to high ammonia concentration, on the other hand, glucose consuming acidogenic bacteria were inhibited.

Isolated pancreatic tuberculosis

We present a case of tuberculosis of the pancreas in a 65 year-old man diagnosed by detection of Mycobacterium tuberculosis DNA in a resection specimen using a highly specific polymerase chain reaction-based assay. Almost all pre-operative and intra-operative findings except for helical computed tomography were highly suggestive of malignant pancreatic tumor. However, the histopathology of the pancreas revealed caseating granulomatous inflammation of possible tuberculous etiology, although special staining and culture of these tissues gave negative results. Only detection of Mycobacterium tuberculosis DNA using the polymerase chain reaction-based assay gave a positive result which allowed antituberculosis treatment to be started. The patient's post-operative recovery has been uneventful without complications. If an early accurate diagnosis can be made in such cases, antituberculosis treatment can be started rapidly.

Liver regeneration after extended right hemihepatectomy in patients with hilar or diffuse bile duct carcinoma

BACKGROUND/AIMS

The degree to which liver size can be restored and the factors that determine liver regeneration after major hepatectomy are not well understood.

METHODOLOGY

Liver volumes (LV) were estimated from computed tomography scans in 16 patients who survived with no evidence of cancer recurrence more than 1 year after extended right hemihepatectomy.

RESULTS

The mean percentage of LV at 1 year was 75.7 +/- 9.5% and LV did not change significantly beyond 1 year after surgery. A significant correlation was observed between LV at 1 year and body surface area (r = 0.79, p < 0.001). A significant inverse correlation was observed between LV at 1 year and the plasma retention rate of indocyanine green at 15 min (the ICG 15 value) (r = -0.72, p < 0.01).

CONCLUSIONS

In adults, the liver does not always regain its pre-operative size after hepatectomy. Patients' body size and intrinsic liver function or liver blood flow, represented by the ICG 15 value, may be related to regenerated liver size.

Staged hepatectomy after emergency transcatheter arterial embolization for ruptured hepatocellular carcinoma

BACKGROUND

Staged hepatectomy after emergency transcatheter arterial embolization (TAE) has been advocated in ruptured hepatocellular carcinoma (HCC). However, there have been no reports of clinical series of this strategy. The purpose of this study was to evaluate the protocol of this therapeutic strategy.

METHODS

Sixteen patients with suspected rupture of HCC were included in the study. After emergency TAE, tumor resectability was assessed, followed by staged hepatectomy or repeated TAE. The patients were reevaluated with regard to rupture of HCCs.

RESULTS

Primary hemostasis was achieved successfully in all patients. Eleven patients were finally judged to have experienced HCC rupture. Seven of them underwent staged hepatectomy; the other four underwent repeated TAE because their tumors were considered unresectable. Survival time tended to be longer, but not to a significant extent, in patients who underwent hepatectomy (range, 139 to 1527 days; median, 375 days) than in those treated by TAE alone (range, 43 to 1317 days; median, 158 days).

CONCLUSIONS

Staged hepatectomy after TAE is a rational treatment for patients with ruptured HCC. Although TAE is highly effective for initial hemostasis, hepatectomy appears to provide better long-term survival.

Staged hepatectomy after emergency transcatheter arterial embolization for ruptured hepatocellular carcinoma

BACKGROUND

Staged hepatectomy after emergency transcatheter arterial embolization (TAE) has been advocated in ruptured hepatocellular carcinoma (HCC). However, there have been no reports of clinical series of this strategy. The purpose of this study was to evaluate the protocol of this therapeutic strategy.

METHODS

Sixteen patients with suspected rupture of HCC were included in the study. After emergency TAE, tumor resectability was assessed, followed by staged hepatectomy or repeated TAE. The patients were reevaluated with regard to rupture of HCCs.

RESULTS

Primary hemostasis was achieved successfully in all patients. Eleven patients were finally judged to have experienced HCC rupture. Seven of them underwent staged hepatectomy; the other four underwent repeated TAE because their tumors were considered unresectable. Survival time tended to be longer, but not to a significant extent, in patients who underwent hepatectomy (range, 139 to 1527 days; median, 375 days) than in those treated by TAE alone (range, 43 to 1317 days; median, 158 days).

CONCLUSIONS

Staged hepatectomy after TAE is a rational treatment for patients with ruptured HCC. Although TAE is highly effective for initial hemostasis, hepatectomy appears to provide better long-term survival.

Plasma concentration of endothelin-1 does not reflect renal vasoconstriction as estimated by duplex ultrasonography in cirrhosis

Endothelin, a potent vasoconstrictor, is thought to play a role in liver cirrhosis-related functional kidney failure. Our aim was to investigate the correlation between renal vasoconstriction, as detected by a Doppler ultrasound technique, and plasma concentrations of endothelin in cirrhotic patients. Fifty cirrhotic patients underwent Doppler examinations to detect renal vasoconstriction. The plasma concentration of endothelin was measured in 10 patients who exhibited vasoconstriction of the renal microvessels diagnosed by Doppler waveform analysis and was compared to that of patients in whom there was no sign of such vasoconstriction. No difference was observed in the plasma concentration of endothelin between patients in whom renal vasoconstriction was diagnosed and those in whom it was not. Our results suggested that the circulating endothelin does not reflect renal vasoconstriction, at least in the early phase of the functional renal failure associated with cirrhosis of the liver.

Preoperative measurement of segmental liver volume of donors for living related liver transplantation

Segmental liver volume determination by computed tomographic scan was carried out preoperatively in nine donors for living related liver transplantation. The calculated volume was compared with the graft size actually obtained by three types of donor hepatectomy. The volume of the left lateral segment (175 to 241 ml) and the left lobe (310 to 490 ml) varied markedly among the donors. The ratio of the left lobar to total liver volume also showed a wide range of values (23.2% to 35.9%). The value of the left lobar volume did not correlate positively with the donor's body weight, suggesting that graft size cannot be predicted only on the basis of the donor's body size. Segmental graft liver volume was estimated by use of computed tomographic scan, with acceptable accuracy on comparison with the graft volume actually obtained. In living related liver transplantation, the type of donor hepatectomy should be selected on the basis of the segmental liver volume of the donor in addition to the recipient's body size so that liver failure can be prevented in recipients and the donor's safety can be assured as far as possible.