Influence of Ozone Application Methods on Efficacy of Ozone Decolorization of Pulp Mill Effluents

This study statistically examined the impacts of ozone application methods on the two representative types of pulp mill effluents. To facilitate statistical evaluation, the experiments were designed as paired block experimental series, and the pooled experimental errors in each block were used for t-test and ANOVA analysis.

Two different ozone application modes were investigated using two specially designed ozone reactor systems. System I consisted of a two-phased reactor which introduced the total amount of ozone to the wastewater in single instance with proper mixing. System II provided ozone to wastewater at a desired rate by controlling the flow and concentration of the ozone/oxygen gas mixture in a once-through flow mode.     

Efficiency Of Ozonation As A Unit Process In The Treatment Of Secondary Effluents From the Pulp And Paper Industry

Experiments were run in a batch reactor on samples of wastewater from pulping processes and paper making after biological treatment (secondary effluent). The samples then were treated in the following technological systems: ozonation alone, ozonation with alum or lime coagulation as a prior step, and ozonation with chlorination as a prior step. Of these, the coagulation-ozonation system was found to be the most effective, yielding high removal efficiencies.     

Effects Of Ozone On Kraft Process Pulp Mill Effluent

Effluent from a kraft process pulp mill was studied in a batch reactor for ozone doses between 50 and 200 mg O₃/L to identify the relative suitability of ozone application locations in the treatment process and see the improvements in biotreatability of wastewaters from a kraft process pulp mill. Laboratory acclimatized seed were used for BOD tests for ozonated and unozonated samples. The inhibitory effects were minimized by using optimum dilutions. The studies were divided into three major sections: characterization of mill effluent; ozone system calibration, and reactor design; and ozonation of mill effluent. Seed for Biochemical Oxygen Demand tests were acclimatized in batch units for primary, bleach and secondary effluents separately. The inhibitory effects which were noted with unacclimatized seed, were reduced by using laboratory acclimatized seed and optimum dilution which were determined during the characterization phase.

The batch reactor designed for the studies consisted of a cylindrical section for holding effluent, and a top spherical section for ozone/oxygen mixture. The reactor proved to be effective for controlling ozone dose. The variation in the applied ozone dose was less than 5 mg/L.

Bleach and primary effluents were treated with 50 and 100 mg/L ozone doses. Duplicate experiments were conducted for these effluents. Secondary effluent was studied for 50,100,150 and 200 mg/L ozone doses. Six replicate experiments were conducted for 50 and 100 mg/L ozone doses, whereas two experiments were carried out for 150 mg/L and one experiment for 200 mg/L ozone dose.

The results were analyzed using 't' test for paired experiments and ANOVA table for statistical confirmation. Residuals were plotted to check the assumptions of constant variance and normal distribution. The results indicated that 50 and 100 mg O₃/L effectively removed color from bleach effluent and primary effluent, but did not significantly change the BOD. Ozone was found to be effective for secondary effluent, as BOD₅ was increased by 65% for 50 and 100% for 100 mg O₃/L doses. The corresponding reduction in color was 62% and 82%, respectively. K_e and L_o values for the BOD equation were calculated by using the non-linear least square method for the BOD equation, giving joint confidence regions for the calculated parameters. It was concluded that ozone is most effective for the removal of color and the increase of BOD in secondary effluent.     

Ozonation Dynamics and Its Implication for Off-Gas Ozone Control in Treating Pulp Mill Wastewaters

Ozonation of biologically pretreated pulp mill wastewaters was studied using both bench and pilot scale fine bubble contactors to determine the oxidation efficiencies, mass transfer coefficients (k_La) and enhancement factors (E) due to the occurrence of chemical reactions. A sensitivity analysis based on the measured process parameters was then used to reveal the interrelated effects of key factors on off-gas ozone concentrations. It was shown that the removal efficiencies of color and AOX were simply related to the amount of utilized ozone, regardless of variation of other operating conditions. Furthermore, the rate of absorption fell within the fast or instantaneous kinetics regimes due to the occurrence of rapid chemical reactions. The Ek_La values were found to vary substantially during the course of ozonation, indicating that the enhancement factors were not only affected not only by operating conditions but also by wastewater characteristics. To effectively control the off-gas ozone emission, measures should be taken to minimize the backmixing, use a counter-current flow arrangement and provide adequate contact time.     

Ozonation as a Treatment for Mechanical And Chemical Pulp Mill Effluents

Eighteen effluent types from seven thermomechanical (TMP), chemithermomechanical (CTMP), bleached chemimechanical (BCMP), and kraft pulp mills were treated in the laboratory with ozone alone or ozone in conjunction with aerobic biological treatment. Except for one mechanical pulp mill effluent, all effluents ozonized showed rapid and selective destruction of their acute toxicity, juvabiones (JB), and resin and fatty acids (RFAs) over biological and chemical oxygen demand (BOD and COD) by ozone. For acute toxicity and RFA/JB removal, aerobic biotreatment of mechanical mill effluent streams produced additive but not synergistic effects when combined with ozone treatment. Ozonation of biotreated kraft effluents yielded substantial decreases in the biologically recalcitrant residual adsorbable organic halogens (AOX), converted COD to BOD, and usually produced large decreases in color.     

Effect of Ozone on Removal of Dissolved Organic Matter and its Biodegradability and Adsorbability in Biotreated Textile Effluents

A study was conducted on the efficacy of ozonation in removing dissolved organic matter (DOM) in biotreated textile effluents and effects on its biodegradability and adsorbability. Results showed the efficient removal of color and fluorescence compounds were achieved through ozonation, due to increasing hydrophilicity and lowering molecular weight of DOM. A significant biodegradability improvement was also observed, and DOM adsorbability on activated carbon was highly dependent on ozone dosage. As the key parameter, consumed 3.8 g O₃/?g TOC₀ was the optimal dosage in the hybrid process combining ozonation with biological activated carbon (BAC) for wastewater reclamation.     

Ozonolysis Of Humic Acid And Its Effect On Decoloration And Biodegradability

The objectives of this research were to investigate the reactivity of humic acid (HA) with ozone and to evaluate its effect on decoloration and biodegradability. Reagent HA was selected as a target compound, and the change in overall water quality parameters, molecular weight distribution, color and biodegradability during ozonation were investigated. Partial oxidation such as decoloration was observed, though the complete destruction represented by TOC removal was not significant. The rate of ozone usage decreased as the reaction proceeded. Degradation to the lower molecular weight fragments was confirmed by ultrafiltration. The close relationship between color and fragmentation was verified. Decoloration was represented by a pseudo-first order reaction. Formic, acetic, oxalic and glyoxylic acids were identified by HPLC and ion chromatography as typical low molecular weight organic acids. The biodegradability of ozonated HA solutions, represented in terms of the ratio of BOD₅ to TOC, was improved.