Aerated hot membrane bioreactor process for treating recalcitrant compounds

A single stage process for continuously biodegrading biochemically oxidizable organic material in a feed comprising dissolved and suspended solids in a wastewater mixture, said process comprising;

• (a) flowing raw waste feed at a rate Q.sub.rw, in combination with from 0% to 200% as much dilution water as feed, the dilution water being fed at a rate Q.sub.d, to an equalizer tank in a pretreatment zone for the raw waste, the zone having a volume sufficiently large to equalize variations in the flow rate of the raw waste to the pretreatment zone which is adapted to remove settlable solids and skimmable free oil, and to withdraw a skimmed feed containing hydrocarbons from the zone;
• (b) removing non-dissolvable and non-emulsifiable solids larger than 106 .mu.m from the skimmed feed and introducing it at a substantially constant flow rate Q.sub.f to a bioreaction zone containing acclimated thermophilic living microorganisms in a mixed liquor;
• (c) aerating the mixed liquor in the presence of the microorganisms at ambient or low pressure, in the range from about 1-5 atm, while maintaining a temperature in the range from 50.degree. C.-60.degree. C., and substantially constant HRT over an arbitrarily long time, longer than either the liquid residence time or the HRT of the bioreaction zone, based on Q.sub.f in the presence of a stable cell population maintained with a regeneration rate no more than 10% greater than the rate at which cells are consumed, and said cells are consumed at a death rate no more than 10% greater than the rate at which they are regenerated;
• (d) flowing a predetermined portion of mixed liquor from the bioreaction zone to a membranous filtration zone so as to generate a rate of flow of permeate greater than Q.sub.f ;
• (e) maintaining a solids concentration of the predetermined portion within predetermined limits without externally hydrolyzing any portion of the mixed liquor;
• (f) recycling a first portion Q.sub.p1 of the permeate to the bioreaction zone;
• and,
• (g) removing a second portion Q.sub.p2 of permeate as reusable and sewerable (to city or municipal sewer system) water;
• whereby, sludge to be disposed of outside said process is less than 20% by weight of the amount one would expect to dispose of in a conventional activated sludge process with the same feed, operating with a mesophilic aerobic bioreactor at a HRT of less than 24 hr.

A two stage process for continuously biodegrading biochemically oxidizable organic material in a feed comprising dissolved and suspended solids in a wastewater mixture, said process comprising;

• (a) flowing said feed at a controlled rate of flow into a substantially mesophilic aerobic reaction zone in a first stage, to provide an essentially constant hydraulic retention time therein, less than 24 hr ("HRT24"), said first stage including a mesophilic aerobic bioreactor (MPB) and a cool mesophilic microfiltration or ultra-filtration membranous filtration zone, and said MPB operates at a temperature in a range from 10.degree. C.-30.degree. C. and ambient pressure with cool mixed liquor having volatile suspended solids (VSS) in the range from 100-25,000 mg/L, said feed having suspended solids smaller than about 180 .mu.m in nominal diameter, an ultimate BOD of at least 100 mg/L and a BOD/COD ratio >0.6;
• (b) flowing a mesophilic concentrate obtained from said cool filtration zone, to an autothermal aerobic reaction zone of a second stage which includes an autothermal aerobic bioreactor (ATAB) and an elevated temperature ("hot") membranous filtration zone;
• (c) maintaining an operating temperature of said MPB within said cool range, to regenerate said cells at a regeneration rate greater than their death-rate so as to have a net production of biomass;
• (d) aerating said suspension in said MPB with enough oxygen-containing gas for utilization by said cells to maintain said regeneration rate;
• (e) flowing said cool mixed liquor through said cool filtration zone at a velocity and pressure sufficient to maintain a predetermined membrane flux in said cool filtration zone, at which flux essentially no solids are retained on the surface of membranes in said cool filtration zone, said membranes having a membrane area sufficiently large to provide a permeate flowing from said cool filtration zone, at a rate chosen to provide said HRT;
• (f) recycling a major proportion of mesophilic concentrate from said cool filtration zone to said MPB as cool concentrate, and flowing a minor portion thereof to said ATAB;
• (g) controlling the flow of said feed to said MPB to provide said controlled rate of flow sufficient to concurrently provide (1) sufficient nutrients to maintain a preselected growth rate of said cells to provide said net production, and (2) enough feed in said mesophilic reaction zone to equal in volume the mount of permeate removed from said first stage;
• and, in said second stage,
• (h) flowing said cool concentrate feed at a controlled rate of flow into said ATAB operating at substantially ambient pressure and at a temperature in a hot range from about 45 .degree. C. to 85.degree. C., With living thermophilic or caldo-active micro-organisms ("hot cells") and suspended solids which said hot cells are adapted to degrade in hot mixed liquor, so as to provide an essentially constant HRT ("HRTA") in the range from 1-12 days, in said ATAB;
• (i) maintaining an operating temperature within said hot range to maintain a predetermined stable population of living cells in said hot mixed liquor, said suspended solids therein having a BOD of at least 20,000 mg/liter;
• (j) aerating said hot mixed liquor with enough oxigen-containing gas to maintain said stable population;
• (k) flowing said hot mixed liquor through said hot filtration zone at a velocity and pressure sufficient to maintain a predetermined membrane flux therein, at which flux essentially no solids are retained on the surface of membranes in said hot filtration zone, said membranes having a membrane area sufficiently large to provide a permeate flowing from said hot filtration zone, at a rate chosen to provide said HRTA;
• (l) flowing hot concentrate from said hot filtration zone into said ATAB as a hot concentrate recycle without thickening or hydrolyzing a portion of said hot concentrate;
• (m) controlling the flow of said cool concentrate to said ATAB to provide said controlled rate of flow sufficient to concurrently provide (1) sufficient nutrients to maintain a preselected growth rate of said hot cells, and (2) enough water in said autothermal bioreaction zone to equal in volume the amount of permeate removed;
• and,
• (n) periodically removing a minor proportion, from 0 to 10% by volume of said hot concentrate recycle to modulate solids content in said autothermal bioreaction zone with essentially no loss of said cells in said mixed liquor, said minor proportion being less than 10% of said biochemically oxidizable material in said feed;
• whereby, sludge to be disposed of outside said process is less than 20% of the mount one would expect to dispose of in a conventional activated sludge process with the same feed, operating with said mesophilic aerobic bioreactor only, at a HRT of less than 24 hr.