Solid waste digestors: process performance and practice for municipal solid waste digestion.

The most common types of anaerobic digesters for solid wastes have been compared based on biological and technical performance and reliability. Batch systems have the most simple designs and are the least expensive solid waste digesters. They have high potential for application in developing countries.

Biodegradation of metal-[S,S]-EDDS complexes.

The [S,S]-stereoisomer of ethylenediaminedisuccinic acid (EDDS), a biodegradable strong metal chelant, has substituted traditional chelants in a number of consumer products. However biodegradability of metal-EDDS complexes has remained largely undocumented. In the present study, activated sludge fed with EDDS as sole C and N source, was shown to readily biodegrade 1 mM pulses of Ca-, Cr(III)-, Fe(III)-, Pb-, Al-, Cd-, Mg-, Na-, or ZnEDDS (the latter only after extensive lag phase).

Decrease of the hydraulic conductivity of sand columns by Methanosarcina barkeri.

The extent to which a methanogen can clog sand columns was examined: two permeameters packed with clean quartz sand were sterilized, saturated with water, inoculated with Methanosarcina barkeri and percolated under upward flow conditions. After approx. 5 months, the hydraulic conductivity of the sand had decreased to 3% and 25% of the highest values measured earlier.

Enhanced dissolution of silicate minerals by bacteria at near-neutral pH.

Previous studies have shown that various microorganisms can enhance the dissolution of silicate minerals at low (<5) or high (>8) pH. However, it was not known if they can have an effect at near-neutral pH. Almost half of 17 isolates examined in this study stimulated bytownite dissolution at near-neutral pH while in a resting state in buffered glucose.

Attachment stimulates exopolysaccharide synthesis by a bacterium.

This study examined the hypothesis that solid surfaces may stimulate attached bacteria to produce exopolymers. Addition of sand to shake-flask cultures seemed to induce exopolymer synthesis by a number of subsurface isolates, as revealed by optical microscopy. Several additional lines of evidence indicated that exopolymer production by attached cells (in continuous-flow sand-packed columns) was greater than by their free-living counterparts.

Relationship between Transport of Bacteria and Their Clogging Efficiency in Sand Columns.

In an earlier article, we reported that, under conditions in which neither exopolymers nor bacterial mats were produced, Arthrobacter sp. strain AK19 was an effective plugging agent in sand columns, whereas the bacterial strain SLI had no significant effect on the permeability of the medium. A laboratory experiment with sand columns was carried out to elucidate the causes of this difference in behavior.

Effect of bacterial extracellular polymers on the saturated hydraulic conductivity of sand columns.

Columns were packed with clean quartz sand, sterilized, and inoculated with different strains of bacteria, which multiplied within the sand at the expense of a continuous supply of fresh nutrient medium. The saturated hydraulic conductivity (HCsat) of the sand was monitored over time. Among the four bacterial strains tested, one formed a capsule, one produced slime layers, and two did not produce any detectable exopolymers.