WE CLAIM:
[Claim 1]
A separation membrane element comprising:
a plurality of separation membranes each having a raw-water-side face and a permeate-side face and forming a separation membrane leaf by being arranged so that the raw-water-side faces face each other;
a permeate-side channel material provided between the permeate-side faces of the separation membranes to form a permeate-side channel;
a raw-water-side channel material provided between the raw-water-side faces of the separation membranes to form a raw-water-side channel; and
a water collection tube for collecting a permeate,
wherein the separation membrane leaf has openings respectively in a peripheral part in a direction perpendicular to a longitudinal direction of the water collection tube, and in an end face in the longitudinal direction of the water collection tube, and
the separation membrane leaf has a width W1 of 150 mm to 400 mm,
the permeate-side channel material has a coefficient of variation in channel width of 0.00-0.10, and the separation membrane leaf has a ratio between the width W1 and a length L of the separation membrane leaf, L/W1, of 2.5 or larger. [Claim 2]
The separation membrane element according to claim 1, wherein the length L of the separation membrane leaf is 750 mm to 2,000 mm. [Claim 3]
The separation membrane element according to claim 1 or 2, which comprises:
a raw-water feed part which is the opening formed in the peripheral part of the separation membrane leaf in the direction perpendicular to the longitudinal direction of the water collection tube; and
a concentrate discharge part which is the opening formed in a one-side end face of the separation membrane leaf in the longitudinal direction of the water collection tube,

the concentrate discharge part being an opening formed by opening a part of the one-side end face. [Claim 4]
The separation membrane element according to claim 3, wherein the raw-water feed part has a length which is 5-35% of the length L of the separation membrane leaf. [Claim 5]
The separation membrane element according to claim 3, wherein the raw-water feed part has a length which is 15-25% of the length L of the separation membrane leaf. [Claim 6]
The separation membrane element according to claim 1 or 2, which comprises:
a raw-water feed part which is the opening formed in a one-side end face of the separation membrane leaf in the longitudinal direction of the water collection tube; and
a concentrate discharge part which is the opening formed in the peripheral part of the separation membrane leaf in the direction perpendicular to the longitudinal direction of the water collection tube,
the concentrate discharge part being an opening formed by opening a part of the peripheral part. [Claim 7]
The separation membrane element according to claim 6, wherein the raw-water feed part has a length which is 10-40% of the length L of the separation membrane leaf. [Claim 8]
The separation membrane element according to claim 6, wherein the raw-water feed part has a length which is 15-20% of the length L of the separation membrane leaf. [Claim 9]
The separation membrane element according to claim 1 or 2, which comprises:

raw-water feed parts which are the openings formed in both end faces of the separation membrane leaf in the longitudinal direction of the water collection tube; and
a concentrate discharge part formed in the peripheral part of the separation membrane leaf in the direction perpendicular to the longitudinal direction of the water collection tube,
the raw-water feed parts being openings formed by opening a part of each of the both ends. [Claim 10]
The separation membrane element according to claim 9, wherein the raw-water feed parts have a length which is 5-45% of the length L of the separation membrane leaf. [Claim 11]
The separation membrane element according to claim 9, wherein the raw-water feed parts have a length which is 15-30% of the length L of the separation membrane leaf. [Claim 12]
The separation membrane element according to any one of claims 1 to 11, wherein the opening in the longitudinal direction of the water collection tube is formed as a single opening extending from an inner end of the separation membrane leaf toward an outside along the direction perpendicular to the longitudinal direction of the water collection tube. [Claim 13]
A method for operating the separation membrane element according to any one of claims 1 to 12, wherein water is fed to the separation membrane element to produce fresh water in an amount which is 35% or more of the water fed to the separation membrane element. [Claim 14]
A separation membrane element comprising:
a plurality of separation membranes each having a raw-water-side face and a permeate-side face and forming a separation membrane leaf by being arranged so that the raw-water-side faces face each other;

a permeate-side channel material provided between the permeate-side faces of the separation membranes to form a permeate-side channel; and
a water collection tube for collecting a permeate,
wherein the permeate-side channel material has a cross-section along a longitudinal direction of the water collection tube, the cross-section having a plurality of channels and having a cross-section area ratio of 0.4-0.75, and
the separation membrane leaf comprises: a raw-water feed part which is an opening formed in a peripheral part of the separation membrane leaf in a direction perpendicular to the longitudinal direction of the water collection tube; and
a concentrate discharge part which is an opening formed in an end-face side portion in the longitudinal direction of the water collection tube.