Shao-Hua Hu

Incineration is a traditional method of treating sewage sludge and the disposal of derived ash is a problem of secondary waste treatment. In this study, sewage sludge ash (SSA) was coated with ferrite through a ferrite process and then used as an adsorbent for ionic dyes (methylene blue [MB] and Procion Red MX-5B [PR]). The modified SSA possessed surface potential that provided electrostatic attraction toward MB and PR. Adsorbent FA10 (named on the basis of being produced from 10 g of SSA in the ferrite process) was used for the adsorption of MB. Ideal pH for adsorption was 9.0 and maximum adsorption capacity based on Langmuir isotherm equation was 22.03 mg/g. Adsorbent FA2.5 (named on the basis of being produced from 2.5 g of SSA in the ferrite process) was used for PR adsorption. Ideal pH for adsorption was 3.0 and the maximum adsorption capacity (calculated as above) was 28.82 mg/g. Kinetic results reveal that both MB and PR adsorption fit the pseudo-second-order kinetic model better than the pseudo-first-order model. The values of activation energy calculated from rate constants were 61.71 and 9.07 kJ/mol for MB and PR, respectively.

Sewage sludge is modified by pretreatment with a synthetic ferrite process, which turns the sewage sludge into an absorbent for ionic dyes and the adsorbent can be removed by a magnetic field. When Fe₃O₄ is synthesized on the surface of sewage sludge, the surface potential of particles is manipulated by adjusting the pH. For Fe₃O₄ synthesis, the molar ratio of Fe²⁺ to Fe³⁺ was 1. In our experiment, two magnetic adsorbents are made (A5 and A10) using 5 g and 10 g doses of sewage sludge, respectively. A5 is used to adsorb Procion Red Mx‐5B (PR) and A10 is used to adsorb Methylene Blue (MB). The specific surface area of A5 is 49.08 m²/g. The ideal pH for PR adsorption is found to be 3 with a maximum adsorption capacity of 0.031 mmol/g (18.83 mg/g). For A10, the specific surface area is 39.84 m²/g, and ideal pH is 6 for MB adsorption with maximum adsorption capacity being 0.078 mmol/g (25.06 mg/g). The kinetics study reveals that MB and PR adsorptions fit well a pseudo‐second‐order kinetic model, and the values of activation energy calculated from the rate constants are 42.82 kJ/mol and 47.19 kJ/mol for MB and PR, respectively. MB and PR adsorption can be characterized as activated chemical adsorption. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 905–912, 2014

Stone processing sludge (SPS) is a by-product of stone-processing wastewater treatment; it is suitable for use as a raw material for making artificial lightweight aggregates (ALWAs). In this study, boric acid was utilized as a flux to lower sintering temperature. The formation of the viscous glassy phase was observed by DTA curve and changes in XRD patterns. Experiments were conducted to find the optimal combination of sintering temperature, sintering time, and boric acid dosage to produce an ALWA of favorable characteristics in terms of water absorption, bulk density, apparent porosity, compressive strength and weight loss to satisfy Taiwan's regulatory requirements for construction and insulation materials. Optimal results gave a sintering temperature of 850 °C for 15 min at a boric acid dosage of 15 % by weight of SPS. Results for ALWA favorable characteristics were: 0.21 % (water absorption), 0.35 %(apparent porosity), 1.67 g/cm3 (bulk density), 66.94 MPa (compressive strength), and less than 0.1% (weight loss).

Paper sludge was pyrolyzed to synthesize an adsorbent for ionic dyes. Two reagents, Methylene Blue (MB) and Procion Red MX-5B (PR), were chosen as adsorbates. Pyrolysis of paper sludge was conducted at 600°C for 1 h under a nitrogen atmosphere, and the carbonized sample was washed with 1 M HCl for 30 min to remove inorganic salts (such as calcium) and to increase the carbon content. Scanning electron microscope (SEM) imaging showed that the particle size of the pyrolyzed paper sludge was obviously reduced when the acid-washing process was applied. Additionally, the specific surface area had increased from 13.25 to 193.86 m2/g. The isoelectric point was around pH 3, which meant the adsorbent revealed positive charge to adsorb anionic dye (PR) when pH was below 3. On the other hand, cationic dye (MB) was adsorbed well under high pH values because of the negative surface charge of the adsorbent. The Langmuir equation was adopted to determine maximum absorption capacity. For MB and PR, the maximum absorption capacities were 119.05 mg/g and 65.79 mg/g, respectively. The adsorption kinetic study revealed that MB and PR adsorptions fit the pseudo-second-order kinetic model well. The activation energies for MB and PR were 12.32 kJ/mol and 2.88 kJ/mol, respectively. The results presented indicate that paper sludge can be pyrolyzed to form a dye adsorbent for cationic and anionic dyes.

Currently, Taiwan's major source of gravel for construction purposes is its river systems; however, over exploitation could potentially deplete this source. To address this problem and reduce dependence on natural aggregate exploitation, this article investigates artificial lightweight aggregates (ALWAs) synthesized from industrial waste such as sewage sludge and sewage‐sludge‐derived ash. The ALWAs were synthesized from the sewage sludge and ash using Na₂CO_3. The sodium carbonate helps produce the required viscous glassy phase (needed for ALWA sintering) at a lower co‐melting temperature than would otherwise be possible. Water absorption, apparent porosity, bulk density and compressive strength of the ALWAs were tested to assess resource‐recycling feasibility. The required dosages of Na₂CO₃ were 16 and 22 wt % for conditioned sludge and ash, respectively. The dosed sludge sample required preheating at 400°C for 0.5 h, followed by sintering at 900°C for 5 min. The ash sample required sintering only at 900°C for 15 min. The sludge‐derived ALWAs gave the following percentages 2.84%, 3.31%, 1.20 g/cm³, and 13.0 MPa for water absorption, apparent porosity, bulk density, and compressive strength, respectively. The corresponding values for ash‐derived ALWAs were: 4.85%, 6.55%, 1.41 g/cm³, and 87.3 MPa, respectively. The characteristics of ALWAs derived in this study were then compared to those of commercially available lightweight aggregates—Lytag and Arlita F7. The characteristics mentioned above of the former were superior than those of the latter except that the value ofdensity was an interval value between Lytag and Arlita. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 740–748, 2013

Paper sludge is a major waste by-product of the paper industry. Its disposal creates serious problems, as approximately 30% of treated sludge is not flammable. In this study, artificial lightweight aggregates (ALWAs) were synthesized from paper sludge by co-sintering with H3BO3. H3BO3acts as a flux to lower the sintering temperature below 900 °C, with co-melting occurring during the procedure. The decomposition gas is sealed within the ALWA during the glassy phase to form a porous structure. Water absorption, apparent porosity, bulk density, compressive strength, and weight loss after rinsing with Na2SO4 were tested to understand the physical properties of the manufactured ALWAs. The optimal method suggested is co-sintering with 18% H3BO3 flux at 890 °C for 30 min. The tested properties mentioned above gave the following results: 4.64 %, 2.77 %, 0.6 g/cm3, 13.2 MPa, and < 0.1 %, respectively. The ALWAs produced in this study have been compared to commercially available lightweight aggregates – Lytag and Arlita – with the examined ALWAs possessing better qualities than Lytag. Water absorption and compressive strength of ALWAs in this study met government requirements of pre-stressed concrete necessary for civil works, and could make useful building material.

This study focuses on artificial lightweight aggregates (ALWAs) formed from sewage sludge and ash at lowered co-melting temperatures using boric acid as the fluxing agent. The weight percentages of boric acid in the conditioned mixtures of sludge and ash were 13% and 22%, respectively. The ALWA derived from sewage sludge was synthesized under the following conditions: preheating at 400 °C 0.5 hr and a sintering temperature of 850 °C 1 hr. The analytical results of water adsorption, bulk density, apparent porosity, and compressive strength were 3.88%, 1.05 g/cm³, 3.93%, and 29.7 MPa, respectively. Scanning electron microscope (SEM) images of the ALWA show that the trends in water adsorption and apparent porosity were opposite to those of bulk density. This was due to the inner pores being sealed off by lower-melting-point material at the aggregates' surface. In the case of ash-derived aggregates, water adsorption, bulk density, apparent porosity, and compressive strength were 0.82%, 0.91 g/cm³, 0.82%, and 28.0 MPa, respectively. Both the sludge- and ash-derived aggregates meet the legal standards for ignition loss and soundness in Taiwan for construction or heat insulation materials.

This study focuses on copper recovery from printed circuit board (PCB) sludge. The copper and other metals in the sludge were extracted with sulfuric acid, and the major metals in the leachate were copper and iron. Jarosite process was utilized to remove impurities such as iron and calcium from the leachate. The elimination percentage of iron from the leachate increased when the molar ratio of potassium/iron (K/Fe) increased in the jarosite process. When the molar ratio of K/Fe was 1.4., it was found that 18.91% of iron content was held while 92.97% of copper content remained in the leachate. The filtrate could be purified further with sulfide precipitation and its filtration characteristics were improved. Then copper sulfide was formed through sulfidation precipitation with a molar ratio of sulfide agent/copper at 0.7; the grade of copper in the recovered material was 57.55%. This indicates that the product was pure CuS, and filtration resistance could be reduced to promote improved copper recovery. © 2011 American Institute of Chemical Engineers Environ Prog, 2011

This study focuses on improving crystalline characteristics of metal‐contaminated sludge. The mineralization behavior of Cu/Al or Cu/Fe coexisting in solution is surveyed, and the characteristics of residue and suspension settling are discussed in the context of water content of residue and settling/specific filtration resistance of suspensions. Experimental data show that the hydrate of Cu₄SO₄(OH)₆ forms during mineralization of copper sulfate solution when hydroxide ion concentration, reaction time, and temperature are not controlled appropriately. Mineral characteristics of the residue are usually poor when the Cu₄SO₄(OH)₆ forms in Cu/Al or Cu/Fe solution. However, Cu₄SO₄(OH)₆ can be further transformed into CuO with wet oxidation or ferrite method, respectively (i.e., mineralization treatment). Water reduction of the residue is from 96.8% to 72.8% in the Cu/Al case or 95.6% to 66.6% in the Cu/Fe case, and the mineralized residue volume is only 1/10 of the hydrate sediment. This is particularly beneficial for sludge disposal. © 2009 American Institute of Chemical Engineers Environ Prog, 2010