US4028238A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Treatment of municipal waste sludges
Assignee: Lancy International Inc
•
Filing: 1975-11-03
•
Granted: 1977-06-07
•
Expires: 1995-11-03
Abstract
Abstract A highly concentrated municipal waste sludge is recovered in a process which involves adding alum and a flocculating agent under alkaline conditions to a dilute waste sludge, adding calcium oxide or hydroxide and filtering the resultant mixture under pressure.
Inventors
- 👤 John L. Allan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 13:24
CPC Classifications
C; C02; C02F; C02F1/00; C02F1/52; C02F1/5236
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
161 words
In a process for dewatering a municipal waste sludge, having a suspended solids content between about 1 and about 5 percent by weight, wherein said sludge is subjected to treatment with sufficient quantities of calcium oxide or hydroxide and from about 5 to about 5000 milligrams alum per liter of waste sludge to obtain a pH value in the range from about 10 to about 11, and a flocculating agent is added thereto in amounts of from about 1 to about 100 milligrams per liter of said waste sludge, whereby a flocculated sludge containing precipitated aluminum hydroxide is obtained, the improvement which comprises: a. adding to the flocculated sludge from about 25 to 75% by weight of calcium oxide or hydroxide based on the weight of suspended solids in the municipal waste sludge before said treatment, and b. filtering the resultant mixture under a pressure of at least about 0.5 atmospheres to obtain a liquid filtrate and a solids filter cake.
Claim 2
Dependent Claim
161 words
In a process for dewatering a municipal waste sludge, having a suspended solids content between about 1 and about 5 percent by weight, wherein said sludge is subjected to treatment with sufficient quantities of calcium oxide or hydroxide and from about 5 to about 5000 milligrams alum per liter of waste sludge to obtain a pH value in the range from about 10 to about 11, and a flocculating agent is added thereto in amounts of from about 1 to about 100 milligrams per liter of said waste sludge, whereby a flocculated sludge containing precipitated aluminum hydroxide is obtained, the improvement which comprises: a. adding to the flocculated sludge from about 25 to 75% by weight of calcium oxide or hydroxide based on the weight of suspended solids in the municipal waste sludge before said treatment, and b. filtering the resultant mixture under a pressure of at least about 0.5 atmospheres to obtain a liquid filtrate and a solids filter cake.
Claim 3
Dependent Claim
20 words
A process according to claim 1, wherein the pressure is in the range of about 10 to about 15 atmospheres.
Claim 4
Dependent Claim
28 words
A process according to claim 1, wherein the filtrate is adjusted to a pH in the range of about 6 to about 9 and released to the environment.
Claim 5
Dependent Claim
16 words
A process according to claim 1, wherein the filter cake is incinerated to recover calcium oxide.
Claim 6
Dependent Claim
21 words
A process according to claim 4 wherein at least a portion of the recovered calcium oxide is recycled to step (a).
Claim 7
Dependent Claim
39 words
A process according to claim 1, wherein the flocculated sludge is allowed to settle and at least a portion of the resultant supernatant liquid phase is removed from the process prior to the addition of calcium oxide or hydroxide.
References Cited (Backward Citations)
GB816399A
Cited
US3171801A
Cited
US3300407A
Cited
US3440166A
Cited
US3472767A
Cited
US3623975A
Cited
US3642619A
Cited
US3997438A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-06-06 | 1980-12-06 | 1981-06-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-06-06 | 1984-12-06 | 1985-06-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-06-06 | 1988-12-06 | 1989-06-07 | $7700.00 | Window Closed / Lapsed |