Schema Vacuuming in Temporal Databases

Temporal databases facilitate the support of historical information by providing functions for indicating the intervals during which a tuple was applicable (along one or more temporal dimensions). Because data are never deleted, only superceded, temporal databases are inherently append-only resulting, over time, in a large historical sequence of database states. Data vacuuming in temporal databases allows for this sequence to be shortened by strategically, and irrevocably, deleting obsolete data. Schema versioning allows users to maintain a history of database schemata without compromising the semantics of the data or the ability to view data through historical schemata. While the techniques required for data vacuuming in temporal databases have been relatively well covered, the associated area of vacuuming schemata has received less attention. This paper discusses this issue and proposes a mechanism that fits well with existing methods for data vacuuming and schema versioning.     

Removal of VUV pre-treated natural organic matter by biologically activated carbon columns

A potential alternative water treatment process using VUV (185 nm+254 nm) irradiation followed by a biological treatment is described. The system uses sufficient VUV radiation (16J cm(-2)) to significantly enhance the production of biologically degradable moieties prior to treatment with biologically activated carbon (BAC). Two similar activated carbons were used, one virgin and one taken from a water treatment plant with an established biofilm. The VUV-BAC process decreased the overall dissolved organic carbon (DOC) concentration of a natural water sample by 54% and 44% for the virgin carbon and previously used BAC, respectively. Furthermore, VUV-BAC treatment decreased the trihalomethane (THM) formation potential (THMFP) by 60-70% and the haloacetic acid (HAA) formation potential (HAAFP) by 74%. The BAC systems effectively removed the hydrogen peroxide residual produced by VUV irradiation. Although nitrite formation can result from VUV treatment of natural organic matter (NOM), none was detected before or after BAC treatment.     

Evaluation of Victorian low rank coal-based adsorbents for the removal of organic compounds from aqueous systems

Three activated carbons and two chars made from low rank coal were evaluated in terms of their ability to remove the organic compound 4-nitrophenol (4-NP) and natural organic matter (NOM) from aqueous systems. The adsorption equilibrium capacities of all adsorbents for 4-NP correlated with the micropore area of the adsorbents. Adsorption rates showed improved removal with decreasing particle size and higher carbon mass loadings. A pseudo first order model was used to fit the kinetic data, with a correlation coefficient of 0.995–0.999 for all systems.

The adsorption capacity for NOM, as measured by UV-absorbing DOC, correlated well with the pore volume and pore surface areas for pores with diameters in the range 2.7–21 nm. The trend in the adsorption capacities and removal rates of the adsorbents for NOM provided evidence that the pore size distribution is one of the most important physical characteristics of activated carbon for the adsorption of NOM.

The performance of activated low rank coal based materials was comparable to a high quality coconut-based commercial carbon in batch systems. Although the non-activated char adsorbents gave poor performance, they have potential for use in applications where poor performance can be outweighed by lower cost.     

Handling discovered structure in database systems

Most database systems research assumes that the database schema is determined by a database administrator. With the recent increase in interest in knowledge discovery from databases and the predicted increase in the volume of data expected to be stored it is appropriate to reexamine this assumption and investigate how derived or induced, rather than database administrator supplied, structure can be accommodated and used by database systems. The paper investigates some of the characteristics of inductive learning and knowledge discovery as they pertain to database systems and the constraints that would be imposed on appropriate inductive learning algorithms is discussed. A formal method of defining induced dependencies (both static and temporal) is proposed as the inductive analogue to functional dependencies. The Boswell database system exemplifying some of these characteristics is also briefly discussed     

Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp

Blooms of toxic cyanobacteria such as Microcystis aeruginosa periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of M. aeruginosa isolated from a wastewater treatment lagoon, and two other algal strains, Anabaena circinalis and Chlorella sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the M. aeruginosa. For M. aeruginosa, for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: A. circinalis > M. aeruginosa > Chlorella sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons.     

The impact of alum coagulation on the character, biodegradability and disinfection by-product formation potential of reservoir natural organic matter (NOM) fractions

Natural Organic Matter (NOM) from Myponga Reservoir, South Australia, was separated into four organic fractions based on their hydrophobic and hydrophilic properties using a sequence of non-ionic and ionic resins. NOM fractions were isolated for the purpose of determining the impact of alum coagulation on removal of these fractions in conventional water treatment, and their potential as precursors in the formation of disinfection by-products (DBP) and in supporting microbial growth. The NOM comprised VHA (very hydrophobic acids), SHA (slightly hydrophobic acids), CHA (charged hydrophilics) and NEU (neutral hydrophilics) fractions. These fractions were then jar tested with alum using low (50 mg/L), operational (100 mg/L) and very high (200 mg/L) doses to assess the removal capacities for these fractions in a conventional treatment plant. High-performance size exclusion chromatography-UV-DOC (HPSEC-UV-DOC) revealed that alum removed more of the hydrophobic and higher molecular weight components of NOM, but less of the NEU fraction and lower molecular weight components of NOM. Determination of biodegradable dissolved organic carbon (BDOC) indicated that the NEU fraction had the highest biodegradability, followed by the CHA, SHA and VHA fractions. The VHA fraction had the highest total-trihalomethane formation potential (t-THMFP), followed by NEU, SHA and CHA. The NOM not removed by alum coagulation had the potential to support microbial growth (NEU fraction), and disinfection by-product (DBP) formation (VHA and NEU fractions). To obtain treated water with lower overall residual NOM, other treatment methods would need to be applied in addition to alum coagulation in order to reduce the concentration of the neutral fraction.     

Removal of dissolved organic compounds in fixed-bed columns: evaluation of low-rank coal adsorbents

Characterisation of a range of Victorian low-rank coal (VLRC) based and commercial adsorbents under continuous flow conditions was conducted in down flow fixed-bed columns. The effect of bed depth, hydraulic loading and initial concentration of the adsorbate 4-nitrophenol (4-NP) was studied. Prediction of the performance of the columns using bed-depth/service time analysis showed good agreement with the experimental results. The VLRC-based activated carbons gave lower service times for removal of 4-NP compared with the coconut-based commercial activated carbon Picactif. However, they showed comparable efficiency in terms of bed volumes treated and carbon usage rate (CUR). The VLRC-activated power station char (APSC) showed the lowest CUR of 0.57 g/L in comparison with 0.62 and 3.61 g/L exhibited by the commercial carbons Picactif and Hydraffin, respectively. The power station char (PSC) and Auschar gave poor CUR of 11.23 and 75.36 g/L, respectively. Three adsorbents were evaluated for the removal of natural organic matter (NOM) from aqueous solution. The breakthrough behaviour indicated that the pore size distribution of the adsorbents is an important physical characteristic for the adsorption of the NOM. There was a non-adsorbable fraction of the NOM that was a function of the type of adsorbent. In the presence of NOM, Picactif gave longer service time for the removal of 4-NP compared with APSC. consistent with the trend obtained in the absence of NOM. However, lower breakthrough times (at 10% C0) of 44 and 47% were obtained for APSC and Picactif, respectively. Further removal (35%) of 4-NP was achieved over extended operation of the beds, however more frequent backwashing was required as a result of the biological growth exhibited in the presence of NOM.