Flock separating apparatus

A flock separating apparatus, has an electrolytic cell (2) fitted with iron electrode and a separating tank (3), wherein the flock is carried upwards by a hydrogen gas produced in electrolysis. The separating tank (3) has a substantially vertical pipe having a length which is at least 10 times, preferably at least 15-20 times more than its diameter.

BACKGROUND OF THE INVENTION 
This application is a 371 application of a U.S. PCT/FI194/00518 
International Application published as WO96/15989 May 30, 1996. 
The present invention relates to a flock separating apparatus for use in 
sewage or sludge treatment, comprising an electrolytic cell and a 
separating tank, into which the flock developed in the electrolytic cell 
is delivered and in which the flock rises up through the action of a gas 
produced in electrolysis. 
The treatment or purification of sewage and industrial process waters is 
conventionally (e.g. International Reference WO 89/06161) carried out by 
using flock separating tanks with air blown therein, so that the rising 
air bubbles carry the lighter solids to the surface as flock which can be 
removed. For example, the Patent publications U.S. Pat. Nos. 4,673,494 and 
4,294,697 disclose such a combination of an electrolytic cell and a 
separating tank such that the electrolytically produced flock can be 
brought up to the surface in the separating tank by means of a gas 
released in electrolysis. Such a combination does not allow the use of 
optimal cell and tank structures and dimensions, resulting in a poor 
separation efficiency. The prior known flock separating tanks are 
relatively shallow and have been aimed at a relatively large surface area. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an improved flock separating 
apparatus, wherein the flock rising speed and a resulting separation 
efficiency have been substantially increased when compared to the prior 
known equipment. 
This object is achieved according to the invention in such a manner that 
the separating tank comprises a substantially vertical pipe, separated 
from an electrolytic cell and having a length which is at least 10 times, 
preferably at least 15 times more than its diameter, and that a feed or 
supply pipe extending from the electrolytic cell to the separating pipe 
opens below the mid-point of the separating pipe, said separating pipe 
having its bottom end connected to a treated-water receiving and discharge 
tank and its top end rising above the surface level of said receiving and 
discharge tank. 
Thus, an important point in the invention is that a hydrogen gas produced 
in electrolysis is used for carrying the flock up in a narrow pipe with a 
high hydrostatic pressure and a high flow rate. Because of a high flow 
rate, the hydrogen gas adhered to flock particles does not have enough 
time to separate and, thus, the hydrostatic pressure in a high separating 
space produces a high rising speed for flock particles. On the other hand, 
the receiving and discharge tank with a sufficiently large surface area 
makes sure, according to the principle of communicating vessels, that the 
water contained in the separating pipe does not pursue a high rising speed 
and comes virtually to a halt at the water level of said receiving and 
discharge tank. Thus, the discharging flock carries along a minimal amount 
of water. 
Although the bottom end of the separating pipe could open directly within 
the opening area of the supply pipe, the separating pipe can be extended 
downwards e.g. for positioning a sand filter in such a manner that 
typically about 1/2-1/8 of the separating pipe length is located below the 
supply pipe opening area.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The water or sludge subjected to a purification treatment is delivered 
through a coarse matter separator 17 and supplied by a pump 1 through an 
electrolytic cell 2 into a separating pipe 3 (see the single Figure). The 
cell 2 is provided e.g. with iron electrodes for passing therebetween the 
water or sludge to be treated. The electrodes are supplied with a direct 
current, the cell being subjected e.g. to the following reactions: 
EQU 2H.sub.2 O.fwdarw.20H.sup.- +2H.sup.+ 
EQU 2H.sup.+ +2e.sup.- .fwdarw.H.sub.2 .uparw. 
EQU Fe.sup.2+ +2OH.sup.- .fwdarw.Fe(OH).sub.2 .dwnarw. 
EQU Fe.sup.3+ +30H.sup.- .fwdarw.Fe(OH).sub.3 .dwnarw. 
The developing hydrogen gas adheres to ferro- and ferrihydroxide deposits, 
which are in turn producing a web or mesh structure for trapping solid 
impurities. This way, the solid matter flocculates and the flock-adhered 
hydrogen gas makes the flock lighter than water. 
Naturally, the iron electrodes can be replaced with other metal electrodes 
as well. In addition or instead of hydrogen, the electrolysis may produce 
other gases as well depending on a liquid to be treated. 
The supply pipe 4 opens into a cone 5 included in the separating pipe 3 and 
is provided at its bottom end with a pipe 6 for collecting and removing 
heavy objects, such as small rocks. The flock particles begin to rise from 
the cone 5 upwards in the pipe 3 at quite a high climbing speed. At the 
top end of said pipe 3 the flock particles pack into a froth-like flock 
deposit which is forced by a conveyor screw 9a into a flock discharge pipe 
7. The pipe 7 carries the flock to a solids separator 8, such as e.g. a 
filter web, a screw press, a separator, a centrifuge or the like. In the 
illustrated case, the separator 8 includes a chute-like filter web 16 and 
a conveyor screw 9b on top of it. The solid matter can be carried e.g. to 
a composter and the liquid can be returned back to the intake side of the 
pump 1. 
In the illustrated case, the separating pipe 3 extends also downwards from 
the cone 5 and, thus, it can be fitted with a sand filter 14. The treated 
water has a passage through ports 15 into a receiving and discharge tank 
10 having a surface area which is multiple compared to that of the 
separating pipe 3. By virtue of this, the climbing speed of water in the 
separating pipe 3 decelerates in relation to the flock climbing speed for 
a further improved separation efficiency. In some cases, the tank 10 may 
simultaneously serve as a storage bin for a liquid to be treated. 
Between the inlet of the supply pipe 4 and the ports 15 said separating 
pipe 3 experiences a flow downwards, the flow rate corresponding to a 
runoff over an edge 11 into a discharge chute 12. The section of the pipe 
3 located below the cone 5 can be replaced with a filter cloth bag for a 
simpler construction. 
The height difference between the overflow edge 11 and a flock discharge 
edge 13 included in the receiving and discharge tank 10 can be made 
adjustable e.g. by providing the pipe 3 with a telescopic top end. By 
adjusting the top end of the pipe 3 (and the pipe 7) downwards it is 
possible to receive wetter flock more quickly. Thus, the overflow edge 11 
must be located slightly below the level of the flock discharge edge 13 
but a substantial distance above the inlet of the supply pipe 4. Since the 
pipes 10 and 3 operate on the principle of communicating vessels, the 
height difference therebetween must be adjusted or balanced in such a 
manner that both experience overflow and the height difference is caused 
or determined by the fact that the flock contained in said separating pipe 
3 is lighter than water as a result of the hydrogen gas adhered thereto. 
Thus, the overflow equilibrium for communicating vessels is achieved by 
means of vessels having different heights. 
The top end of the separating pipe 3 can be provided with a duct for the 
discharge of hydrogen gas. In major plants, the hydrogen gas can be 
recovered. It is also possible to recycle the hydrogen gas back into the 
separating pipe 3 below the cone 5. Of course, it is possible to supply 
compressed air to the bottom end of the pipe 3 or to include a sand filter 
14 in the bottom end of the pipe 3 below the cone 5. The necessity of 
these extra arrangements depends on an intended application. The invention 
can be exploited both in a small and a large scale operation. The possible 
large-scale applications include both industrial waste waters and 
community sewage. The possible smaller scale applications include e.g. 
agricultural farms. 
In major plants, it is possible to connect several pieces of such equipment 
in line e.g. such that the top ends of separating pipes 3 included in 
different pieces of equipment are connected to a common flock discharge 
pipe 7. The invention has already been practically tested in the 
purification treatment of liquid manure in a hog farm. Hence, it was found 
out that the great length of separating pipe 3 in relation to the diameter 
is a particularly critical factor in view of securing a sufficient 
climbing speed and separation efficiency. In addition, the large surface 
area of tank 10 in relation to the surface area of pipe 3 was found 
advantageous in that water separates effectively from flock instead of 
pursuing to rise into the flock discharge pipe 7. 
The invention is not limited to the particular details of the apparatus 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described apparatus without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpretend as illustrative and not in a limiting sense.