Nutrient release from fish silage using microwave-enhanced advanced oxidation process.

The microwave-enhanced advanced oxidation process was used to treat fish silage for nutrient release and solids reduction prior to its use as a fertilizer for greenhouse operations. Fifteen sets of experiments with varying hydrogen peroxide dosages and treatment temperatures were conducted to evaluate the effectiveness of the process on the solubilization of fertilizer constituents. It was found that up to 26% of total Kjeldahl nitrogen could be released as ammonia with 6% hydrogen peroxide dosage at 170 degrees C. An increase of nitrate/nitrite concentration was observed with higher hydrogen peroxide dosage and higher microwave temperature; the highest concentration of 10.2 mg L(- 1) nitrates/nitrites was achieved at at 170 degrees C and 6% H(2)O(2) dosage. Up to 20 +/- 9.5% of total chemical oxygen demand was reduced at temperatures between 120 and 170 degrees C. Large quantities of volatile fatty acids were generated at lower temperatures, corresponding to an increase in soluble chemical oxygen demand, but not at higher temperatures. The treatment of fish silage using the microwave-enhanced advanced oxidation process appears to be promising.

Solubilization of blood meal to be used as a liquid fertilizer.

The solubilization of blood meal by means of the microwave-hydrogen peroxide enhanced advanced-oxidation process (MW/H(2)O(2)-AOP) was studied. It was found that over the treatment temperature range of 60 to 120 degrees C, solids particle reduction, ammonia and orthophosphate production could be achieved by this process. Large protein molecules were broken down into intermediate compounds with low molecule weights, ammonia and nitrate. Intermediate compounds, such as peptides and amino acids, can also be easily converted to nitrogenous nutrients for plant growth by bacteria. Soluble nitrogen content increased with an increase in microwave heating temperature when acid was added; significant amounts of ammonia were obtained at higher temperatures. Nitrate decreased in concentration with an increase of treatment temperature. Orthophosphate concentrations increased after the advanced-oxidation process (AOP) treatments, with and without acid addition; but were more pronounced with acid addition. Maximum solubility of chemical oxygen demand (COD) occurred at 80 degrees C. Without the addition of acid, soluble COD decreased due to protein denaturation and coagulation out of the solution.

Sludge reduction and volatile fatty acid recovery using microwave advanced oxidation process.

Sewage sludge was subjected to the combined microwave-hydrogen peroxide-sulfuric acid enhanced advanced oxidation process (MW-H(2)O(2)-H(+)-AOP) to evaluate the potential of reducing suspended solids in sludge. The soluble chemical oxygen demand (SCOD) and acetic acid produced were dependent on the amounts of H(2)O(2) and acid used in the process. For sewage sludge, a higher volume of H(2)O(2) addition not only favored the destruction of sludge solids, but also conserved the carbon content in the medium. Volatile fatty acid (VFA) concentrations also increased with the amount of inorganic acid in the solution. For the soluble fraction of solutions derived from microwave-treated sludge, over 96% of the total COD was in the soluble form, and up to 25% of this soluble COD was acetic acid. The presence of an inorganic acid was a stability factor in retaining the SCOD in solution, instead of the formation of carbon dioxide, resulting in reduced total COD in the solutions. By controlling the amounts of H(2)O(2) and acid addition, the MW-H(2)O(2)-H(+)-AOP could solubilize and/or reduce the sludge mass.

Sewage sludge nutrient solubilization using a single-stage microwave treatment.

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 hydrogen peroxide/ microwave advanced oxidation process for sewage sludge treatment.

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.