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The microwave enhanced advanced oxidation process (MW-AOP) has been applied to pre-treat different sludge types and high solids content. Secondary sludge not only had the highest solids and nutrient content but also yielded higher treatment efficiency than primary or mixed sludge. In the case of secondary sludge with 4% total solids (TS), the total suspended solids (TSS) concentration was reduced by 32% while soluble chemical oxygen demand concentration increased from 1% to 40% after treatment at 110°C. A high level of nutrient release was also achieved; about 65% total phosphate (TP) solubilized at 110°C. The degree of secondary sludge disintegration was dictated by temperature and hydrogen peroxide dosage. The optimal operating temperature for the system was 110°C, and sludge containing TS up to 8% was treated effectively. Secondary sludge with 8% TS had a TSS reduction of 41% after treatment at 110°C while COD solubilization was about 45%; about 55% TP was solubilized at 10 min holding time. Treatment of sludge with higher solids content would allow for handling larger amounts of sludge at a given period and reduce heating cost per unit of treated sludge. The inter-relationship between the degree of sludge disintegration and changes in chemical and physical properties was also clearly demonstrated here. The treated sludge would be an ideal substrate for anaerobic digestion or phosphorous recovery processes. High levels of nutrients (phosphorus and nitrogen) and metal release, and solids disintegration from sludge containing high solids content would make subsequent resource recovery processes more effective and economical.

Mixtures of fats, oils and grease (FOG) either with dairy manure or with thickened waste secondary sludge (TWSS) were treated using microwave enhanced advanced oxidation process (MW-AOP). For both dairy manure and TWSS mixtures, the maximum increase in soluble COD (SCOD) resulted from the 1:1 mixture by total solids (TS) weight. In the TWSS mixtures, production of volatile fatty acid (VFA) increased with greater FOG content, while there was a decreasing production trend in VFA in dairy manure mixtures. Nutrients and metals were also released for all sets. The degradation followed peroxidation mechanism to produce lower molecular weight substrates such as short-chain fatty acids which would be less inhibitory to microbes. Nutrients and metals in the treated solution would sustain microbial growth in a biological system. FOG content for the mixtures in the MW-AOP treatment should be less than 75% by TS weight to prevent oxidation to CO

Three sludge types (primary sludge, secondary sludge, and anaerobic digested sludge) and centrate produced from a local municipal wastewater treatment plant were treated by the microwave enhanced advanced oxidation process. All sludge types exhibited a certain degree of solids solubilization and phosphorus release, as well as altered physical properties after the treatment. The extent of treatment was influenced by the inherent characteristics of sludge itself, besides the treatment process conditions, such as temperature and hydrogen peroxide dosage. The microwave enhanced advanced oxidation process was very effective for the treatment of all types of sludge for purpose of solids solubilisation, and nutrients release for resource recovery. Very high soluble chemical oxygen demand concentrations (62%) and total suspended solids reduction (75%) were obtained in the treated secondary sludge conducted in the pilot-scale continuous-flow system. The microwave enhanced advanced oxidation treatment system shall be used for treating both primary and secondary sludge, and therefore, the system shall be installed in the treatment train after an aerobic biological treatment system, and before an anaerobic digestion system to gain the maximum process efficiency.

This study investigated the effectiveness of bench and pilot-scale microwave enhanced advanced oxidation process (MW-AOP) for treatment of sewage sludge in neutral, acidic (pH 4) and alkaline (pH 9) conditions. The MW-AOP treatments were very effective: total suspended solids reduction and chemical oxygen demand solubilization were better in the sets at pH 9 than at pH 4. Alkaline conditions would be more favorable for the subsequent anaerobic digestion for biogas production. Release of orthophosphate, particle size distribution, dewatering properties and settling of the sets at pH 4 were better than at pH 9. The supernatants obtained from the sets at pH 4 had a high orthophosphate concentration and a low total suspended solids content, which were more suitable for struvite (a fertilizer) recovery process. Energy consumption was lower for the pH adjusted treatment sets compared to those of MW only and MW-AOP at neutral conditions; energy for the pH adjusted sets varied between 0.32 and 0.41 kWh/L of sludge treated. The results indicated that the MW-AOP could reduce the volume of sludge for disposal, and produce a high quality treated effluent suitable for further resource and energy recovery. Depending on the needs of each wastewater treatment plant’s treatment priority, the experimental conditions applied in the process can be adjusted accordingly.

Liquid organic fertilizers (LOFs) are relatively easier to degrade than those of solid organic fertilizers, and the nutrients are readily available for plant uptake. Microwave enhanced advanced oxidation treatment (MW/H2 O2 -AOP) was used to convert solid organic fertilizers (insoluble blood meal, bone meal, feather meal, sunflower ash and a mixture) into LOF.; Results: After the MW/H2 O2 -AOP treatment, high soluble nitrogen (11-29%), soluble phosphorus (64%) and potassium (92%), as well as low total suspended solids content could be obtained. The resulting LOF would make the nutrients more bioavailable, and would provide some of them for the plant uptake immediately. Temperature and hydrogen peroxide dosage were found to be significant factors affecting nitrogen release from blood meal and feather meal, while temperature and pH were found to be significant factors for solubilizing phosphorus and potassium from bone meal and ash, respectively.; Conclusion: The MW/H2 O2 -AOP reduced suspended solids, and released nutrients into solution; therefore, it was an effective treatment method to make LOFs. © 2016 Society of Chemical Industry.; © 2016 Society of Chemical Industry.

A newly designed continuous-flow 915 MHz microwave wastewater treatment system was used to demonstrate the effectiveness of the microwave enhanced advanced oxidation process (MW/H2O2-AOP) for treating dairy manure. After the treatment, about 84% of total phosphorus and 45% of total chemical oxygen demand were solubilized with the highest H2O2 dosage (0.4% H2O2 per %TS). The reaction kinetics of soluble chemical oxygen demand revealed activation energy to be in the range of 5–22 kJ mole−1. The energy required by the processes was approximately 0.16 kWh per liter of dairy manure heated. A higher H2O2 dosage used in the system had a better process performance in terms of solids solubilization, reaction kinetics, and energy consumption. Cost-benefit analysis for a farm-scale MW/H2O2-AOP treatment system was also presented. The results obtained from this study would provide the basic knowledge for designing an effective farm-scale dairy manure treatment system.

The microwave-enhanced advanced oxidation (MW/H2O2-AOP) treatment of sewage sludge in a continuous-flow 915 MHz microwave system was studied. A higher H2O2 dosage at the same flow rate resulted in better solids disintegration in terms of higher soluble chemical oxygen demand. The highest soluble chemical oxygen demand concentration of 5174 mg/L was obtained at a dosage of 0.005 L/L (0.5 % v/v). A higher soluble chemical oxygen demand was obtained at a higher flow rate with the same H2O2 dosage. A substantial amount of soluble phosphorus (over 60 % of total phosphorus content) was produced for all treatments, regardless of H2O2 dosage. A first-order reaction kinetics of soluble chemical oxygen demand was proposed in this study. Real-time energy consumption corresponding to performance efficacy, which provides a realistic assessment of the process efficiency, was calculated. Energy consumption was found to vary between 0.22–0.29 kWh/L of sludge treated. The results demonstrated that a continuous-flow 915 MHz microwave system resulted in high treatment efficiency in terms of nutrient release, solids disintegration, and low energy consumption, which is suitable for real-time industrial applications.

The microwave enhanced advanced oxidation process (MW-AOP) was used to treat dairy manure in a continuous-flow 915 MHz microwave wastewater treatment system. The treatment efficiency increased with an increase in temperature, as well as hydrogen peroxide dosage. The settling property was also improved in all treated sets, regardless of temperature applied. The system operated at temperatures100 °C had a much higher soluble chemical oxygen demand than at temperatures100 °C. The highest soluble carbonaceous compounds, orthophosphate and ammonia were obtained at 110 °C and 0.6%H

Fats, oils, and grease (FOG) and source separated organics (SSO) were treated with the microwave-enhanced advanced oxidation process (MW-AOP) at 90 and 110 °C, with varying amounts of hydrogen peroxide dosages. The treatment efficiency, in terms of soluble substrates and volatile fatty acids (VFA), increased with an increase in both temperature hydrogen peroxide dosages. Fatty acids and compounds with carbonyl group and/or hydroxyl group in both initial and treated FOG samples were identified by gas chromatography-mass spectrometry. MW-AOP treatment temperatures and hydrogen peroxide dosages dictated the formation of degradation products. The degradation followed peroxidation mechanism to produce lower molecular weight substrates such as short chain fatty acids which would be less inhibitory to microbes. After the MW-AOP treatment, both SSO and FOG comprised of more soluble and low molecular weight compounds. These compounds included VFA and nutrients that would be readily available for bacterial or plant uptake.

A novel technology involving radiofrequency heating and hydrogen peroxide (RF/H 2 O 2 ) was used for the treatment of dairy manure. RF/H 2 O 2 process efficacy was affected by power intensity, hydrogen peroxide dosage and holding time. The optimal conditions for nutrient release and solids disintegration were determined: for orthophosphate release, power intensity of 3 kW/L (kW/L substrate treated), holding time of 65 min and H 2 O 2 dose of 1%; and power intensity of 1.9 kW/L, holding time of 53 min and H 2 O 2 dose of 1.2% for soluble chemical oxygen demand concentration. The results indicated that the treatment efficacy of radiofrequency process was comparable to microwave process. However, the radiofrequency process required a longer holding time than microwave process. Nevertheless, energy required by the radiofrequency was lower than microwave as the radiofrequency system was capable of handling higher volumes of manure with higher solids content at a given time.

An innovative radiofrequency oxidation technology was developed to treat organic slurries with high solids content. The extent of nutrient release and solids disintegration from separated solids fraction of dairy manure was examined in a pilot scale 6 kW radiofrequency system. The factors affecting the process were hydrogen peroxide dosage, heating time and power intensity of radiofrequency. The newly developed RF oxidation process was highly efficient in releasing orthophosphate and soluble chemical oxygen demand in the treated solution and found to be viable to treat dairy manure.

Aerobic sewage sludge and dairy manure were pre-treated by conventional heating (CH) (40, 50 and 60°C) followed by microwave enhanced advanced oxidation process (MW/H2O2-AOP) at 100 and 120°C for solids disintegration and nutrient release. Increasing CH and MW temperatures resulted in an increase in soluble chemical oxygen demand concentration and volatile fatty acids in the treated solution. The maximum ratio of soluble to total chemical oxygen demand obtained for sewage sludge and dairy manure was 60% and 22%, respectively. The synergistic effect of microwave irradiation and hydrogen peroxide (H2O2) was more pronounced for sewage sludge at high CH and MW temperatures. Temperature and treatment time played a significant role in releasing orthophosphates. A maximum orthophosphate-to-total phosphate ratio of 55% and 85% was obtained for sewage sludge and dairy manure, respectively. A simple energy balance reveals that the CH step proves to be advantageous during continuous real-time operation of MW/H2O2-AOP technology.

A pilot-scale continuous-flow 915-MHz microwave enhanced advanced oxidation (MW/H2O2-AOP) treatment system was specifically designed and used for the treatment of sewage sludge. The focus o...

A H2O2 dosing strategy for microwave enhanced advanced oxidation process treatment of sewage sludge was formulated. The timing of hydrogen peroxide introduction in a continuous-flow 915-MHz system affected the treatment efficiency in terms of solids destruction, nutrient release and volatile fatty acid (VFA) production. Introducing hydrogen peroxide into the treatment set at 60°C was found to be more effective than adding it at the beginning. The treatment set with hydrogen peroxide introduced at 60°C resulted in higher soluble chemical oxygen demand concentrations and VFAs, higher soluble total Kjeldahl nitrogen and soluble total phosphate and also improved dewaterability and settling. However, there were no differences in terms of ammonia and orthophosphate release between the two treatment schemes. It is an advantage to introduce hydrogen peroxide into the treatment set at 60°C in a continuous-flow microwave system.

A continuous flow mode of the microwave enhanced advanced oxidation process (MW/H2O2-AOP) was used for sludge treatment as opposed to a batch operation mode from past studies. The effects of pre-microwave heating, microwave irradiation and post-microwave holding on organic matter solubilization were studied. Pre-microwave heating did not improve the overall orthophosphate solubilization, but helped in organic matter solubilization. Nutrients and organic matter were found to have increased during the post-microwave holding period, indicating overall sludge solubilization can be more effective when maintained at a high temperature after treatment with the MW/H2O2-AOP. It was beneficial to operate a continuous mode of the MW/H2O2-AOP at a longer retention time for organic matter solubilization, and at a shorter retention time for orthophosphate solubilization. Sludge settleability was greatly improved with the microwave treatment, with or without the addition of H2O2. The pre-heating of sludge before treatment with the microwave process by the means of heat exchange can be beneficial for the overall organic matter solubilization in the MW/H2O2-AOP.

This study was undertaken to evaluate the efficiency of a liquid-solids separation process and microwave pretreatment, as well as anaerobic biodegradability of microwave pretreated dairy manure. Liquid-solids separation of raw dairy manure resulted in solid and liquid fractions having different properties, with the solid fractions richer in total and volatile solids content and liquid fractions richer in nutrients and metal ions. Substantial amounts of soluble chemical oxygen demand and nutrients were released into the solution after the microwave treatment. The microwave pretreated dairy manure was also subjected to anaerobic digestion. The kinetic parameters of methane production potential, maximum methane production rate and lag time were determined using the modified Gompertz equation. Anaerobic digestion of liquid manure, without microwave treatment, outperformed the sets with microwave treatment. The microwave-treated liquid dairy manure, without acid addition had better results in terms of methane potential and methane production, than with acid addition. Thermophilic digestion exhibited a higher maximum methane production rate than that of mesophilic digestion, but lower methane yields. The microwave pretreatment of dairy manure resulted in high soluble chemical oxygen demand; however, methane yield was not increased.

This study investigated the treatment of dairy manure using the microwave enhanced advanced oxidation process (MW-AOP) at pH 2. An experimental design was developed based on a statistical program using response surface methodology to explore the effects of temperature, hydrogen peroxide dosage and heating time on sugar production, nutrient release and solids destruction. Temperature, hydrogen peroxide dosage and acid concentration were key factors affecting reducing sugar production. The highest reducing sugar yield of 7.4% was obtained at 160°C, 0 mL, 15 min heating time, and no H(2)O(2) addition. Temperature was a dominant factor for an increase of soluble chemical oxygen demand (SCOD) in the treated dairy manure. The important factors for volatile fatty acids (VFA) production were microwave temperature and hydrogen peroxide dosage. Temperature was the most important parameter, and heating time, to a lesser extent affecting orthophosphate release. Heating time, hydrogen peroxide dosage and temperature were significant factors for ammonia release. There was a maximum of 96% and 196% increase in orthophosphate and ammonia concentration, respectively at 160°C, 0.5 mL H(2)O(2) and 15 min heating time. The MW-AOP is an effective method in dairy manure treatment for sugar production, nutrient solubilisation, and solids disintegration.

The microwave enhanced advanced oxidation process (MW/H2O2-AOP) aided with dilute sulfuric acid was applied in a two-stage treatment of dairy manure for nutrient release, solids reduction, and reducing sugar production. A much higher hydrogen peroxide dosage (1.2 g H2O2/g TS) was used in Stage 2 than that in Stage 1 (0.38 g H2O2/g TS). Most of the reducing sugar was produced in Stage 1, and only a small amount produced in Stage 2. The highest reducing sugar yield of 15.5% was obtained at 160℃, 0 mL H2O2/, and 20 min of heating time. With a high hydrogen peroxide dosage and a higher operating temperature of 160℃ in Stage 2, the nutrient release conversion rate was much higher in Stage 2 than Stage 1. All of total phosphorus was converted to orthophosphate, and a very high ammonia concentration was obtained in the treated solution. The results indicated that the MW/H2O2/-AOP operated under the reducing process (without hydrogen peroxide) provided the best yield of reducing sugar; however, when operated under an oxidative process (with hydrogen peroxide), it favoured nutrient release and solids disintegration. The concentration of total chemical oxidation demand (TCOD) in the treated solution decreased with an increase of temperature, hydrogen peroxide dosage and heating time. Soluble chemical oxidation demand (SCOD) concentration decreased with a very high hydrogen peroxide dosage. Volatile fatty acids (VFA) concentration decreased with an increase of hydrogen peroxide dosage. Ammonia and orthophosphate concentrations increased with an increase of temperature and hydrogen peroxide dosage.

A pilot-scale (5 kW) 915-MHz microwave-enhanced advanced oxidation process (MW/H2O2-AOP) was custom designed and tested to treat dairy manure. The objective of the study was to verify the performance efficiency of the new system in terms of nutrient release, solids disintegration and energy consumption and compare it with an existing pilot-scale (5 kW) 2450-MHz microwave system. The 915-MHz MW/H2O2-AOP resulted in a release of about 60% of total phosphorus as orthophosphate, and about 25% of total chemical oxygen demand was disintegrated in the treated solution. The treatment performance was similar to that of 2450-MHz MW/H2O2-AOP albeit using lower H2O2 dosage. Research and development work currently underway with the 915-MHz MW/H2O2-AOP will optimise the treatment and energy efficiency.

This study investigated the feasibility of treating the foams generated in enhanced biological phosphorus removal processes with the microwave-enhanced advanced oxidation process to reduce solids and solubilize nutrients for recovery purposes. It was found that more than half of the total chemical oxygen demand was solubilized during the treatment with just a small dose of hydrogen peroxide, signifying effective destruction of foam solids. Significant solubilization of phosphates, volatile fatty acids and ammonia was also observed, along with the release of metals contained in the foam, including calcium, potassium, and magnesium, which thereby represents additional potential benefits for nutrient recovery via subsequent crystallization processes. Since the solids content of foam is typically high, pretreatment for thickening sludge solids is not necessary prior to the use of microwave-enhanced advanced oxidation processes. As a result, this also offers further potential for reduction of energy costs. The process could be an efficient method for the removal and control of foam and the recovery of all available phosphorus at the same time.

The microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was used to treat separated solid dairy manure for nutrient release and solids reduction. The MW/H(2)O(2)-AOP was conducted at a microwave temperature of 120 degrees C for 10 minutes, and at three pH conditions of 3.5, 7.3 and 12. The hydrogen peroxide dosage at approximately 2 mL per 1% TS for a 30 mL sample was used in this study, reflecting a range of 0.53-0.75 g H(2)O(2)/g dry sludge. The results indicated that substantial quantities of nutrients could be released into the solution at pH of 3.5. However, at neutral and basic conditions only volatile fatty acids and soluble chemical oxygen demand could be released. The analyses on orthophosphate, soluble chemical oxygen demands and volatile fatty acids were re-examined for dairy manure. It was found that the orthophosphate concentration for untreated samples at a higher % total solids (TS) was suppressed and lesser than actual. To overcome this difficulty, the initial orthophosphate concentration had to be measured at 0.5% TS.

BACKGROUND: Microwave-enhanced advanced oxidation processes with and without the addition of ferrous sulfate (MW/H2O2/Fe2+-AOP and MW/H2O2-AOP respectively) were studied for reduction of solids and solubilisation of nutrients from secondary sewage sludge. RESULTS: For the MW/H2O2/Fe2+-AOP the yields of solubilisation of orthophosphate and ammonia decreased with increasing temperature. The best results (88.1 mg L−1 for orthophosphate and 22.7 mg L−1 for ammonia) were obtained at a treatment temperature of 40 °C. In contrast, the MW/H2O2-AOP had an advantage when it was operated at higher temperatures of 60 and 80 °C. The highest yields of solubilisation were obtained at 60 °C for orthophosphate (81.1 mg L−1) and at 80 °C for both ammonia (35.0 mg L−1) and soluble chemical oxygen demand (1954 mg L−1). Over the temperature range used in this study, the MW/H2O2-AOP gave a better performance than the MW/H2O2/Fe2+-AOP. CONCLUSION: For sewage sludge treatment the MW/H2O2-AOP is more effective than the MW/H2O2/Fe2+-AOP in terms of solid reduction and nutrient solubilisation. It will also be more cost-effective, as it does not require iron addition in the process. Copyright © 2008 Society of Chemical Industry

This study explored the applicability of a pilot-scale continuous-flow radiofrequency (RF) heating system to treat sewage sludge by the RF-oxidation process (RF/H2O2). Depending on temperature and hydrogen peroxide dosage, high amounts of soluble chemical oxygen demand and volatile fatty acid were produced, and phosphates, nitrogen, and metals were solubilized. A high temperature and/or a higher H2O2 dosage implemented in this system yielded high solubilization of organic matters. Orthophosphate increased with an increase in treatment temperature up to 60°C, its concentration decreased as temperature further increased. There was little effect on orthophosphate release by varying H2O2 dosage. The efficiency of the RF/H2O2 process was comparable to the microwave (MW) enhanced advanced oxidation process (MW/H2O2-AOP), in terms of solids disintegration and nutrient release; however, the solubilization rate was lower for RF/H2O2 process. The overall energy consumed by the RF/H2O2 process was higher than the MW/H2O2-AOP.

Solids destruction and nutrients release from sewage sludge were investigated using thermal destruction and/or oxidation processes. Hydrogen peroxide (H(2)O(2)), ozone (O(3)) and a combination of both were used for the oxidation processes performed at ambient temperature. Thermal destruction using microwave (MW) alone without an oxidant was also conducted. Microwave enhanced advanced oxidation processes (MW-AOP), such as MW/O(3), MW/H(2)O(2) and MW/H(2)O(2)/O(3), were conducted at 100 degrees C. In terms of nutrients release and solids reduction, the MW/H(2)O(2)/O(3)-AOP yielded the best result; an addition of ozone improved the MW-AOP process. More than 30% of TP and 20% of TKN were released into the solution. About 37% of total COD was also solubilized from sludge mass. Both the conventional oxidation processes and the MW-AOP processes could be used to release nutrients and to reduce solids from sewage sludge; however, the MW-AOP processes were superior in performance. Microwave heating alone also resulted in a substantial amount of ortho-phosphate into the solution.

The effects of an advanced oxidation process combining microwave, hydrogen peroxide and acid hydrolysis in a single stage (MW/H2O2/H+ -AOP) on the process efficiency of sewage sludge treatment and nutrient recovery were investigated. At lower temperature regimes (60-80 degrees C), the soluble phosphate was substantially higher in a two-stage process than in a single stage MW/H2O2/H+ -AOP process. However, higher soluble phosphate concentration was obtained for single-stage treatment at the higher operating temperature regimes (100-120 degrees C). With the addition of an inorganic acid, a very high yield of soluble phosphate was obtained in the solution at 120 degrees C. In tests with acid addition, soluble ammonia increased as temperature increased. For single stage MW/H2O2/H+ -AOP, maximum soluble ammonia was obtained at 120 degrees C. Significant concentrations of soluble COD were also obtained in this treatment. A threshold temperature of 80 degrees C was observed, at which all of the COD could be solubilized. However, at higher temperatures (100-120 degrees C), further oxidation processes occurred to form carbon dioxide, resulting in decreased amounts of soluble COD in the solution.

A full-scale sequencing batch reactor (SBR) system was evaluated for its ability to remove carbon and nitrogen from swine wastewater. The SBR was operated on four, six-hour cycles each day, with each cycle consisting of 4.5 hours of "React," 0.75 hours of "Settling", 0.75 hours for "Draw" and "Fill." Within each cycle, an amount of wastewater equivalent to about 5% of the reactor volume (5,500 litres) was removed and added. The SBR system was able to remove 82% of biochemical oxygen demand (BOD) and more than 75% of nitrogen. Even though the SBR effluent, with an average effluent BOD5 of about 588 mg L(-1), did not meet the discharge criteria, it enabled a reduction of the land base required for land application of swine wastewater by about 75%. Results indicated that the SBR system was a viable method for the treatment of swine wastewater.

A novel thermal–chemical treatment technology using radiofrequency heating and oxidants (hydrogen peroxide, ozone and a combination of both) was used for the treatment of sewage sludge. This was to evaluate the process effectiveness on cell disintegration and nutrient release of sludge, physical property changes such as particle size distribution, dewaterability and settleability, and their inter-relationships. The effectiveness of treatment processes was in the following order, from the most to least: thermal–oxidation process, oxidation process and thermal process. The thermal–oxidation process greatly increased cell disintegration and nutrient release, improved settleability, and decreased particle sizes. The treatment scheme involving ozone addition followed by hydrogen peroxide and radiofrequency heating yielded the highest soluble chemical oxygen demand, volatile fatty acids, ammonia and metals, while proffering the shortest capillary suction time and excellent settling properties.

The focus of this study was to investigate the combined effects of hydrogen peroxide concentration and acid hydrolysis on ammonia and ortho-phosphate solubilization for subsequent struvite formation. A lower microwave temperature regime between 60 and 120 °C was of interest in this study because of the greater amount of polyphosphates found in the treated secondary sludge at these temperatures. At microwave-heating temperatures of 100 °C and 120 °C, it was found that increasing the hydrogen peroxide concentration resulted in an increased phosphorus and ammonia solubilization. At a reaction time of only 5 min, the combination of hydrogen peroxide and acid hydrolysis resulted in up to 61% of total phosphorus and 36% of TKN released into solution, as soluble ortho-phosphate and ammonia, respectively. The amount of soluble nitrogen in solution after microwave treatment was found to increase with the hydrogen peroxide concentration. Up to 39% of the total soluble nitrogen could be released into solution. Furthermore, the addition of hydrogen peroxide resulted in a dramatic decrease in the PO4:NH3 molar ratio, an important factor controlling struvite formation. In terms of facilitating poly-P breakdown into ortho-phosphate in the acid hydrolysis process, hydrogen peroxide was found to be the most effective at 80 °C and at a concentration of 1.5 wt% H2O2. At temperatures of 100 and 120 °C, the amount of soluble ortho-phosphate increased with the hydrogen peroxide concentration. Key words: advanced oxidation process, ammonia nitrogen, hydrogen peroxide, microwave, phosphorus release, sludge, struvite.

This study focused on the efficacy of the microwave/hydrogen peroxide advanced oxidation process (MW/H2O2-AOP) on the secondary sludge treatment. The results indicated that at temperatures of 80 degrees C and above, essentially all of the chemical oxygen demand (COD) was solubilized by the combined MW/H2O2-AOP. This process also solubilized nutrients (nitrogen, phosphorus and metals) from sludge which can be extracted for other purposes, such as struvite crystallization. Based on a stoichiometric molar ratio of 1:1:1 for Mg:NH3:PO4, ammonia was found to be the limiting nutrient without any H2O2 addition in the process at all temperatures. With the addition of H2O2, ortho-phosphate became the limiting nutrient. In all treatments, magnesium was non-limiting, thus magnesium addition is not required for subsequent struvite crystallization. The MW/H2O2-AOP also enhanced the pasteurization or sterilization of sludge. The MW/H2O2-AOP provides novel sludge management options for the wastewater industry, not only in solubilization of carbon for further methane production, but also in nutrients extraction for crystallization for use as fertilizer.

Both the advanced oxidation process (AOP) using a combination of hydrogen peroxide addition and microwave heating (H2O2/microwave), and the microwave heating process were used for solubilization of phosphorus from liquid dairy manure. About 80% of total phosphate was released into the solution at a microwave heating time of 5 min at 170 degrees C. With an addition of H2O2, more than 81% of total phosphate could be released over a reaction period of 49 h at ambient temperature. The AOP process could achieve up to 85% of total phosphate release at 120 degrees C. The results indicated that both the microwave, and the AOP processes could effectively release phosphate from liquid dairy manure. These processes could serve as pretreatments for phosphorus recovery from animal wastes, and could be combined with the struvite crystallization process to provide a new approach in treating animal wastes.

A closed-vessel microwave digestion process for the determination of total Kjeldahl nitrogen (TKN) has been developed for sewage and wastewater. TKN values obtained from the microwave digestion method were in excellent agreement with those of the thermal digestion method. The accuracy of both analytical methods is comparable. In comparison to the conventional thermal digestion, the microwave method shortened the time required for complete digestion from 4 h to 25 min, and also decreased the maximum digestion temperature from 380 degrees C to 200 degrees C. This developed method may contribute to a significant reduction in sample digestion time, resulting in an increase in analytical throughput. The microwave digestion method developed in this study could be a rapid and efficient means for TKN determination for sewage wastewater and sludge.

A novel microwave treatment of sewage sludge was developed as part of the ongoing studies for enhancing the recovery of phosphorus from municipal wastes. The microwave treatment provided a rapid and efficient process to release phosphate from sewage sludge. By using the microwave treatment for only 5 min, up to 76% of the total phosphate in the sludge could be released into the solution. No chemical additions were necessary in the microwave process. After the sewage sludge was microwave treated at a temperature of 100 °C, no microbial activities were observed over a period of 24 h. This microwave process could also be used for the conditioning and stabilization of liquid sludge. Key words: microwave technology, phosphate release, conditioning and stabilization of sludge.

As part of on-going studies related to development–implementation of new technologies and approaches for enhancing recovery of phosphorus from municipal wastes, the effectiveness of various methods of pretreating waste activated sludges (WASs) from a biological nutrient removal (BNR) process was investigated to determine suitable methods for maximizing phosphorus release. The additions of a strong base (NaOH), strong acid (HCl), organic acid (citric acid), and sodium acetate to waste sludge all facilitated the release of phosphate into solution. The maximum phosphate release was obtained by adding 4.9 mmole/L (~400 mg/L) of acetate to an intermittently mixed digester. Excess amounts of acetate did not further increase the phosphate concentrations. Acetate addition, which triggers carbon storage, a unique characteristic of enhanced biological phosphorus removal (EBPR) processes, releases internally stored phosphate compounds and is recommended as a method for releasing phosphates from EBPR sludges. Along with phosphates, various cations (most notably magnesium and potassium) were also mobilized and released into solution during digestion using acetate. These ions can be beneficially reused for struvite crystallization. Key words: acetate addition, caustic addition, phosphorus release, P-solubilization, sludge treatment, struvite.

Phosphorus was recovered from dairy manure via a microwave-enhanced advanced oxidation process (MW/H2O2-AOP) followed by struvite crystallization in a pilot-scale continuous flow operation. Soluble phosphorus in dairy manure increased by over 50% after the MW/H2O2-AOP, and the settleability of suspended solids was greatly improved. More than 50% of clear supernatant was obtained after microwave treatment, and the maximum volume of supernatant was obtained at a hydrogen peroxide dosage of 0.3% and pH 3.5. By adding oxalic acid into the supernatant, about 90% of calcium was removed, while more than 90% of magnesium was retained. As a result, the resulting solution was well suited for struvite crystallization. Nearly 95% of phosphorus in the treated supernatant was removed and recovered as struvite.

This study carried out in a full-scale fish waste composting facility examined the effects on the ‘active’ stage of composting of two bulking agents (alder and fir), and two amendments (peat moss and vermiculite). The rise in temperature which occurred as composting progressed was accompanied by an increase in ammonia and volatile fatty acid production. This overall pattern was observed in all four mixes, whereby the concentrations of ammonia and volatile fatty acids increased rapidly and then declined gradually over the course of monitoring. The changes in their concentrations over time proved to be a reliable indicator of the progress of the composting process. Ammonia emissions from the composting piles were reduced by the additions of peat moss, vermiculite, and alder, in comparison to the headspace ammonia level for the fir mix. The results indicated that ammonia management during the composting process could be easily accomplished by the use of suitable amendments or bulking agents. Peat moss and vermiculite were found to be good amendments for fish composting and alder was found to be a good bulking agent.

This study, which used data obtained from samples from a full-scale fish waste composting facility, examined the effect on the ‘active’ stage of composting when the weight ratio of bulking agent to fish was varied. Two weight ratios of bulking agent to fish wastes were tested experimentally (1:1 and 1·3:1). A monitoring strategy was adopted which used the concentrations of ammonia and volatile fatty acids as the major indices of the progress of the composting process. A headspace-gas chromatograph technique developed in the Bio-Resource Engineering laboratory was used to monitor the concentrations of volatile fatty acids. Both mixes satisfied the temperature requirements for the destruction of pathogens and, in both cases, total carbon declined gradually over the course of monitoring. A similar overall pattern was observed for both mixes in terms of a correlation between rises in temperature and increases in ammonia and volatile fatty acid production. However, a significant difference was recorded for the ammonia and volatile fatty acid concentrations of the two mixes, with higher concentrations recorded for the 1·3:1 mix in both cases. This indicated that while both mixes composted well, the 1·3:1 mix did so more efficiently. Using the concentrations of ammonia and volatile fatty acids as major indices of the effectiveness of the active process proved to be a valuable monitoring strategy. The headspace analysis technique was a simple and effective method for determining the volatile fatty acid concentrations. Traditional indicators of moisture content, pH and temperature should also be monitored.

Laboratory-scale experiments were undertaken to investigate aeration and air stripping as methods for removing ammonia from swine wastewaters with high nitrogen concentrations. The effects of temperature, air to liquid flow ratio and pH were investigated using wastewaters with a range of solids concentrations and pH values. Five sets of aeration experiments were carried out using two identical 3 l reactors made of acrylic tubing. For the air-stripping experiments, two identical stripping towers were constructed out of acrylic tubing and packed with plastic rings. At a pH of 11·2, the aeration method took approximately 150 h to achieve 90% removal efficiency. This was achieved with temperatures of 22°C and a low air flow rate of 1·15-1·60 l/min. At a comparable pH (11·5), the best results for the air-stripping method achieved 90% removal with only 7 h of treatment. This result was obtained with wastewater temperatures at 22°C, as in the aeration experiment, but the air flow rate was much higher at 90 l/min. Results showed that at a pH of 9·5 and 10·5, ammonia removal efficiency was directly dependent upon the air and liquid influent temperatures. However, at a pH of 11·5 there was no appreciable improvement with a rise in air and influent temperatures. The results further showed that an influent with a low pH required a longer period of time to achieve the same treatment efficiency. A pH of 10·5 is recommended as the most efficient of those tested, as very high levels of nitrogen removal were obtained at that level without incurring problems of excess lime. The high ammonia removal efficiency of the air-stripping method indicates that it could provide an interim solution for current waste management problems in the swine industry.

The concentrations of phytotoxic organic acids and phenols in a compost produced from salmon farm mortalities (morts) were investigated as indices of compost maturity. A recently developed headspace-gas chromatograph (HS-GC) technique was used to determine the concentrations. A modified static pile method was employed in this composting study. Three different weight ratios of morts to sawdust were used in two separate runs, as were different configurations of layers of the composting materials. After 60 d of active composting with aeration, the products from Run 1 were stored without aeration, while aeration was continued for 6 h daily to those from Run 2. HS-GC analysis of these products showed very high concentrations of organic acids and a significant amount of phenol. The trend was for the phytotoxic organic acids and phenol to decrease as storage time increased. Organic acids and phenol disappeared much more slowly for the non-aerated products than for the aerated ones. The concentrations of organic acids and phenol served as a more reliable indicator of the degree of maturity of the composts than did moisture content, pH or the carbon to nitrogen ratio. The headspace analysis technique provided a relatively simple and effective method for the detection of these phytotoxic components of fish composts. Results also showed that the distribution of morts and sawdust within composting piles was important.

A study was undertaken to examine the effect of storage temperature on the malodour of swine slurry. Two storage temperatures were tested, ambient temperature (22–25°C) and 4°C. The effects of the storage on both the separated solids from the slurry and on the filtered slurry were included so as to ascertain which fraction of the slurry contained the major portion of malodorous compounds. The process was monitored by using a static headspace sampling gas Chromatograph (HS‐GC) technique which recorded the changes in the concentrations of the major malodorous compounds in swine slurry, volatile fatty acids, phenols and indoles. Results showed the effect of temperature on the storage of slurry, filtrate and solids to be significant in the initial 40 days. They also revealed that the malodorous compounds were primarily to be found in the soluble fraction of swine slurry. An initial accumulation and later depletion of the VFAs, phenols and indoles in the slurry, filtrate and solids indicated that the ...

Two hybrid upflow anaerobic sludge blanket (UASB) reactors were used to treat screened swine wastewaters. In order to achieve the advantages of both suspended growth and attached-growth anaerobic reactor systems, this type of reactor has a rope matrix inserted as a fixed-film medium in its mid section. The study examined the reactor performance in terms of its treatment efficiency and membrane production, and evaluated the effect which the absence of seeding in the start-up process had on the efficiency of reactor performance. The conclusion reached was that this hybrid UASB reactor could be used without seeding in the treatment of screened swine manure if the organic loading rates were moderate. Under these conditions, over 57% COD removal and 0.71 litres CH 4 /litre reactor day were obtained. While sludge loss did occur, methane production increased and the concentrations of VFA in the effluents were kept below 100 mg/litre. It is believed that the additional biofilm in this hybrid reactor increased the stability of the reactor and helped maintain steady methane production. The results also confirm that granulation of the sludge is an essential requirement for satisfactory operation.

This study investigated the effectiveness of composting fish-farm mortalities using a layering method. This is a modified static-pile method that avoids the need to mix the initial raw materials by piling alternate layers of morts and bulking agent. The use of different ratios of morts to sawdust was investigated. Temperature profiles and volumetric shrinkage were monitored to assess the progress of the composting process. The quality of the composts after 60 days was assessed on the basis of the carbon/nitrogen ratio and moisture, ammonia, nitrate and organic acid contents. The results indicate that within the range of fish morts to sawdust ratios tested, whole fish were completely composted and thermophilic conditions attained, thus satisfying the EPA PFRP temperature requirements. The temperature profiles indicate that the distribution of morts and bulking agent within layers was important: thinner layers of morts improved the temperature profiles. The 3:1 mix was judged to be the most advantageous, since it allows more morts to be composted per unit area.

Static headspace sampling and gas chromatograph (GC) analyses were used to monitor the concentrations of malodorous compounds (volatile fatty acids (VFA), phenol, p-cresol, indole, and skatole) throughout the aerobic treatment of swine wastewater. In two sets of experiments, continuous aeration of the wastewater was carried out for 24 h. An addition of sodium azide, a microbial inhibitor, was made in the second experiment in order to explore the impact of microbial activity versus air stripping on the concentration of volatile compounds. The study confirms that static headspace sampling and GC separation provide a useful method for monitoring the treatment process. Results also confirm that aeration is an effective method of odour control for swine wastewaters. Under aerobic conditions, malodorous VFA, phenol, p-cresol and skatole were degraded. The significant decline in the rate of degradation of acetic acid in the second experiment can be attributed to a decline in microbial activity.

Chemical treatment processes can be applied in conjunction with physical and biological processes to effectively treat swine wastewaters. This study investigated the optimum dosage and the effectiveness of five different chemical treatments on low, medium and high strength wastewaters. Effectiveness was measured primarily in terms of suspended and total solids removal, and biological and chemical oxygen demand reduction. Phosphate removal was also measured but not optimized. The results showed that for all wastewater strengths, a low dosage of the polymer PERCOL 728 was the most effective. This polymer was excellent at solids removal, increasing the removal efficiency by approximately 20%. It was also effective at reducing the biological and chemical oxygen demands of the wastewaters. However, PERCOL 728 was the least effective of the chemicals in the removal of PO4‐P; lime and alum proved more effective than FeCl3 in this capacity. The PO4‐P removal trend was for efficiency to increase with dosa...

This study examined the composting of swine wastes in a modified static pile system. Variations in the heights of the reactors and differences in the initial moisture contents of the compost mix were the variables under consideration. The effectiveness of the process was assessed on the basis of the physical parameters of temperature, moisture content, particle size distribution, shrinkage and compaction. The reactor with a compost pile height of 1.0 m had the best results with both initial moisture contents. However, the results for all the reactors improved when the initial moisture content was lower. This suggests that although the reactor with a pile height of 2.3 m gave the least favourable results, control of aeration and initial moisture levels could make this height of composting pile effective.

The effects of various bulking agents were examined on the efficiency of composting the fibrous solids obtained from swine manure after a liquid/solids separation process. The effects on the quality of the resulting composts were also examined. The separated solids were either composted without bulking agents, or mixed with different portions of peat moss and/or sawdust. Aeration rates were also varied in different experimental sets. A self-heating mode of operation was adopted. The results indicated that the fibrous solids from a liquid/solids separation process could be composted in small reactors with or without the addition of bulking agents. The composting masses reached thermophilic temperatures (45-70°C) and met regulatory requirements with or without aeration. Aeration rates of 0·04 to 0·08 l/min per kg volatile matter and an intermittent mode of aeration are recommended for the composting of separated swine manure. Based on measured compost characteristics and composition, the finished composts made from a manure/peat moss mixture had the best quality in terms of moisture content, nitrogen content, carbon-to-nitrogen ratio and colour of the product.

Silage production using salmon farm mortalities was carried out in the laboratory to test the effect of temperature on silage stability, liquefaction levels and soluble nitrogen levels. Citric acid, formic acid and a mixture of the two were used as ensiling media. The silages were stored at two different temperatures (5°C and 22°C). The results show that temperature has a considerable influence on the stability, liquefaction and soluble nitrogen levels of the salmon silage. For the same acid mixtures and concentrations, silages stored at 5°C had a much lower pH value than those stored at 22°C. With a storage temperature of 5°C, the acid concentration can be as low as 0·75% citric acid/0·5% formic acid, 1% formic acid or 4·5% citric acid. At 5°C, such silages can be safely stored for at least 100 days; at 22°C, they would only remain stable for about 30 days. Both the liquefaction and soluble nitrogen levels of the silages stored at 5°C were found to be significantly lower than those of the silages stored at 22°C.

A two-stage, modified static pile method of composting fish mortalities was tested for the effects of pile height on both the process and product quality. Two sets of compost runs were conducted with the volume of fish mortalities composted in the second set double that of the first. This was accomplished by increasing the height of the compost pile without increasing the cross-sectional area. The results indicate that this height increase had no significant effect on the quality or the maturity of the fish compost after 4 months of active composting. Differences in the temperature profiles of the piles did occur; with the taller pile, it took longer for the temperature to rise to thermophilic levels as well as to cool to ambient temperatures. Aeration had little consistent or significant effect on the compost quality, the volatile fatty acid concentrations or on the temperature profiles of the different runs.

A study was undertaken to investigate magnesium sulfate as a precipitation reagent for the treatment of highly concentrated swine wastewaters. The effects of pH and of the dosage of magnesium sulfate on the removal efficiencies of ammonia and phosphate were studied. The pH is a factor in the removal efficiency of phosphate and ammonia. In this study, the highest phosphate removal was achieved at pH 9, while the highest ammonia removal occurred at pH 11. Results show that magnesium sulfate could be used on its own to remove phosphate and ammonia. However, due to low efficiencies of magnesium sulfate in the removal of concentrated solids, a polymer (PERCOL 728) was also tested as a co-precipitation reagent. The results indicated that a combination of magnesium sulfate and PERCOL 728 could be used to reduce phosphate, ammonia and solids concentrations. A dosage of 50 mg 1 −1 of PERCOL 728 and 1000 mg 1 −1 of MgSO 4 reduced phosphate levels from 479 to 6 mg 1 −1 , and suspended solids from 1.8% to 0.2%.