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Ammonia (NH3) stripping by microwave irradiation was used to increase the efficiency of anaerobic digestion. The effects of final temperature (FT) (80 ≤ FT ≤ 100°C) and microwave irradiation time (...

This study detetmined optimal microwave irradiation (MI) conditions for removal of ammonia nitrogen (NH3-N) from swine wastewater. The wastewater was treated using a laboratory-scale indust...

This work experimentally determined the effect of thermal and microwave pretreatments on the anaerobic digestion of mixtures of municipal primary and secondary sludges in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 20, 15, 10, 7, and 5 days. The ratio of soluble chemical oxygen demand (COD) to total COD in thermally pretreated and microwaved sludges at 80°C was 2.7 and 3.2 times higher than that of raw sludge, respectively. The volatile solids (VS) and COD removal efficiencies in all three di gesters fed with raw (control), thermally pretreated (TM), and microwaved (MW) sludges decreased as the HRT was reduced. The highest relative improvement in VS removal compared to the control occurred at the HRT of 5 days in the TM and MW (29 and 41% higher than the control, respectively). At this HRT, improvement in the COD removal efficiencies in the TM and MW compared to the control was 28 and 53%, respectively. Improvements in biogas production compared with the control increased in both the TM and MW as the HRT was reduced to 5 days. The relative improvement in daily biogas production compared to the control from the TM and MW was 33 and 53% higher than the control at the HRT of 5 days, respectively. The results show that microwave pretreatment is more effective than thermal pretreatment in increasing the solubilization degree and mesophilic anaerobic biodegradability of sewage sludge.

In this paper, we quantify the effect of heating pretreatment on the degree of solubilization of waste activated sludge. The pretreatment process was carried out using a lab-scale industrial microwave unit (2450 MHz frequency). Response surface analysis was applied to determine the combination of output power (400-1600 W), target temperature (60-120 degrees C), and total solid concentration (1-3% total solid (TS)). The power, temperature, and TS concentration significantly affected the solubilization degree of sludge. Within the design boundaries, the conditions predicted to maximize the solubilization degree of 17.9% were determined to be 400 W, 102 degrees C, and 2.3% TS.

This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of municipal secondary sludge. Sludge samples (500 g) were heated for 0, 3, 5, 7, 9, 11, and 15 min in a microwave oven (2450 MHz, 700 W). The solubilization degree (soluble chemical oxygen demand (SCOD)/COD) of sludge increased asymptotically with microwave irradiation time from 2% at 0 min to 22% at 15 min. The concentrations of soluble protein, carbohydrate, lipid, and calcium also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) of sludge increased from 3.58 to 4.77 g COD l −1 . The results show that microwave irradiation increases the solubilization degree and BAP of municipal secondary sludge.

Solubilization of sewage sludge creates favorable conditions for anaerobic microorganisms to produce biogas. In this paper, we quantify the effect of heating pretreatment on the degree of solubilization of sewage sludge. The pretreatment process was carried out using a lab-scale industrial microwave unit (2450 MHz frequency). Response surface analysis was applied to determine the combination of temperature-increase rate (ramp rate) (2.9 to 17.1℃/min) and terminal temperature (52 to 108℃). Both ramp rate and temperature significantly affected the solubilization degree of sludge. Within the design boundaries, the conditions predicted to maximize the solubilization degree of 15.8% were determined to be 2.9℃/min and 104℃.

The research reported in this paper determined the effect of combined microwave irradiation and NaOH pretreatment on solubilization and biodegradation in anaerobic digestion of waste-activated sludge (WAS). Solubilization increased significantly with NaOH concentration (20–60 meqNaOH/L) and microwave final temperature (100–170°C). However, the experimental trials did not adequately approximate the response surface for volatile solids reduction, cumulative biogas production, and biogas yield. Within the design boundaries, the maximum solubilization degree (72%) of WAS occurred at 60 meq/L and 170°C. The highest volatile solids removal efficiency (62.4%) was achieved at 40 meq/L and 170°C. Cumulative biogas production and yield were 2.3–5.7 L/L and 154–393 mL/g added volatile solids, respectively, and both parameters were highest at 20 meq/L and 135°C.

A series of experiments with 0, 1, 3, 5, and 7 g Ca 2+ /l using calcium chloride were performed to evaluate the effect of various calcium concentrations on anaerobic digestion of swine wastewater. The addition of 3 g/l gave the best performance. On the other hand, the calcium concentrations of 5–7 g/l had an inhibitory effect on anaerobiosis. The lag phase durations expected in biogas production were 28–31 days with the addition of 0–3 g/l of calcium, and 43–52 days for calcium concentrations of 5 g/l or more. The concentrations of total volatile fatty acids decreased to less than 100 mg/l with calcium concentrations of 3–7 g/l. On the other hand, propionate and i -valerate concentrations remained over 4 and 0.8 g/l, respectively, when 1 g/l or less of calcium was added.

This work experimentally determined the effect of microwave irradiation on the anaerobic digestion of municipal secondary sludge in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 15, 10 and 5 days when microwaves were used as a heating source. A microwave-heating anaerobic digester (MHAD) was compared with a water-heating reactor (control). Biogas production increased in both digesters as the HRT decreased except for the control with a HRT of 5 days. Improvement in removal efficiency of volatile solid and biogas production of the MHAD relative to the control increased as the HRT decreased. The results show that the MHAD was more effective than the control in increasing mesophilic anaerobic biodegradability and biogas production treating secondary sludge.

This work experimentally determined the effect of microwave irradiation with NaOH pretreatment on anaerobic digestion of thickened waste activated sludge in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 15, 10, 7, and 5 days. The degree of substrate solubilization was 18 times higher in pretreated sludge (53.2%) than in raw sludge (3.0%). Removal efficiency of volatile solid in digesters fed with raw (control) and pretreated sludges (PD) decreased as HRT reduced. The highest relative improvement of properties compared with the control occurred at 5 day HRT. Improvements in biogas production compared with the control increased in the PD as HRT was reduced to 5 days (205% higher at 5 days). However, digested sludges in the control and PD increased capillary suction time compared with raw sludge. The results show that microwave irradiation combined with alkali pretreatment is effective in increasing mesophilic anaerobic biodegradability of sewage sludge.