Q Zhou

Screening tests for assessing treatability of inorganic industrial wastes by stabilisation/solidification with cement

Stabilisation/solidification with cementitious or pozzolanic binders (S/S) is an option for reducing leachability of contaminants from residual, predominantly inorganic, industrial wastes and contaminated soils before disposal or reuse. Treatment by S/S is complicated by the fact that the presence of impurities, such as the contaminants and bulk matrix components present in industrial wastes, can have deleterious effects on cements. Therefore, careful laboratory development and testing of S/S formulations are required prior to full-scale application, to avoid technology failures, including problems with handling and contaminant retention. An understanding of cement chemistry and contaminant immobilisation mechanisms has been used to propose a series of test methods and performance thresholds for use in efficient evaluation of the treatability of industrial wastes by S/S, and optimising S/S formulations: measurement of stabilised/solidified product workability, bleeding and setting time (for flowable mixtures) or Proctor compaction (for compactable mixtures), together with unconfined compressive strength, leachability in a batch extraction with distilled water, and hydraulic conductivity.

Development of process envelopes for cement-based stabilisation/solidification of metal treatment filtercakes

Treatment by stabilisation/solidification with cement-based binders (S/S) is an option for wastes that cannot be prevented or reduced, such as metal treatment sludges from a variety of industries. A laboratory research project at University College London (UCL) is being conducted to generate a coherent body of data regarding S/S of metal treatment filtercakes, with the intention of investigating relationships between engineering and leaching properties and stabilised/solidified (s/s) product composition.This paper reports on the results from application of screening tests (consistence, bleeding, setting time, unconfined compressive strength (UCS), distilled water extraction, hydraulic conductivity) to more than 40 s/s products containing four different metal treatment sludges treated with four different binder systems. The threshold values of the key properties can be used to define process envelopes that describe the limits of applicability of S/S to the chosen waste types.This investigation of metal treatment filtercakes is part of the ProCeSS project, which is being conducted by a consortium of five universities and 17 industrial partners, under the UK DIUS Technology Strategy Board (TP/3/WMM/6/I/15611).

Biochemical and microbial contamination of surgical devices: A quantitative analysis

Reusable devices are required to be safety processed prior to patient use, including cleaning and disinfection and sterilization. In developing and testing cleaning processes, it is important to understand the levels of soils typically present on devices after surgical use. Previous soil investigations have focused on microbial contamination levels; less is known about biochemical contamination. In this study, microbial and biochemical contamination on a range of surgical instrumentation after patient use were investigated. Analysis included bacteria levels, total organic carbon, protein, and hemoglobin. The highest levels of soil contamination were caused by protein, in contrast with bacteria levels being a minor component of instrument soiling. This study provides a better understanding of the microbial and biochemical levels of soils that are typically present in used surgical devices. These levels can be used to develop artificial test soils for testing cleaning efficacy under laboratory conditions and to further evaluate patient risks from inadequate cleaning.

The application of GAC sandwich slow sand filtration to remove pharmaceutical and personal care products

Lab-scale GAC sandwich slow sand filters with different GAC layer depths were evaluated for the first time to remove selected pharmaceutical and personal care products (PPCPs) (namely DEET, paracetamol, caffeine and triclosan, 25 μg/L). Coarse sand (effective grain size of 0.6 mm) was used instead of conventional fine sand. In addition to single sand and GAC filters, GAC sandwich filters were assessed at three filtration rates (i.e. 5 cm/h, 10 cm/h and 20 cm/h) to compare removals. Sandwich filter with 20 cm GAC achieved the best average PPCP removal (98.2%) at 10 cm/h rate. No significant difference of average PPCP removal was found between 10 and 20 cm/h filtration rates for the three GAC sandwich filters (p > 0.05). Among the selected PPCPs, DEET, the recalcitrant compound, was most effectively removed by the GAC sandwich filters. Combining the GAC layers with the slow sand filters significantly enhanced the removal of the target PPCP compounds (p < 0.05), demonstrating that both adsorption and biodegradation contributed to the removals. Furthermore, pseudo-second-order equation (Type 1) could best represent the adsorption kinetics of the four target PPCP compounds onto GAC. In relation to other quality parameters, sandwich filter with 20 cm of GAC also showed good average removals of chemical oxygen demand (COD) of 65.8% and total organic carbon (TOC) of 90.3%, but occurrence of ammonium up to 0.76 mg/L concentration indicated inapplicability of filtration rate of 5 cm/h. No significant difference was found between 10 cm/h and 20 cm/h filtration rates for nitrogen and phosphate removals (p > 0.05). Results of this lab-scale investigation show that GAC sandwich slow sand filter is potentially an effective process for removing PPCPs from tertiary wastewater.

Species-specific interaction of trihalomethane (THM) precursors in a scaled-up distribution network using response surface methodology (RSM).

ABSTRACT Response surface methodology (RSM) with central composite design (CCD) was used to monitor and optimize species-specific interaction of trihalomethane (THM) precursors in a scaled-up distribution network (DN). Independent variables such as applied chlorine (Cl2), contact time (t), humic acid (HA) and bromide ions (Br−) were analyzed using full factorial CCD. Analysis of variance revealed a good agreement between experimental data and proposed a two-factor interaction model (p = .04, R2 = 0.7983). As a precursor, Cl− and Br− interaction with HA affected THMs’ speciation. These precursor molecules were perceived least significant as discrete elements but HA: Br− and pH product significantly impacted total trihalomethane (TTHM) formation (r = 0.998, p = .007). This mutual interactive fraction was observed pH-dependent and influenced TTHM yield. Dibromochloromethane and bromoform formation was observed pH-dependent provided sufficient Br− in the system. Applied chlorine had significant (p = .01), while time had insignificant (p = .75) effect. Multiple response optimization suggested pH range between 6.0 and 7.6 and HA: Br− ratio between 1.3 and 5.9 were satisfactory for maintaining TTHM below ≤80 μg/L in DN with 0.88 desirability function (D). Their respective concentration may be minimized by changing precursor’s individual concentration and possible combinations.