Photosynthetic Yields and Byproduct Recovery
527
aluminium from the algae slurry would reduce overall coagulant requirements as the
aluminium could be recycled and reused as a primary flocculant. Aluminium remaining in
the algae has been shown to be toxic to chickens ingesting the product at 6% dietary
levels (Rachapaetyakom and McGarry, 1971). It was therefore considered desirable to
remove aluminium from the product.
Aluminium extraction by acidification was investigated (Fig. 5). This technique has
been used in water treatment practice (Roberts and Roddy, 1960). Methods used in our
laboratory comprised pond water flocculation and settling in 6-litre jars, algal slurry
separation by supernatant decantation, acidification using sulphuric acid and alum
recovery by vacuum filtration.
Preliminary tests revealed that the appropriate pH range during acidification for
recovery was pH 3 to 4.5. Within this range aluminium recovery varied between 1 l%and
71% (Fig. 6). Physical damage to the algal cells was observed at pH levels below 3. Some
aluminium was lost in the supernatant, much of it in the form of visible unsettled floes.
These could be recovered at the prototype plant scale by dual media filtration. For the
purpose of these studies the aluminium lost with the supernatant was considered as a loss
from the system. pH 3.6 was chosen as the optimum pH in view of algal product quality
and economics of recovery.
After entering the continuous recycle system some of the aluminium is lost to the
flotation units underflow, and some to the algal product; the remainder is recycled.
Aluminium losses from the system continue with subsequent recycles. After many cycles,
very little of the original aluminium remains within the system. The fraction of original
aluminium remaining after n recycles may be estimated as Y n = R
n , where R is the
fraction recovered by acidification. The average number of passes which aluminium
makes through the system is 1/(1—R). Thus if 70% recovery is achieved only 0.3% of the
original aluminium would remain in the system after ten recycles, the average number of
recycles being 3.3 for such a system.
In order to study recovery and flocculating characteristics of recovered aluminium the
continuous recycle process was simulated by semi-batch technique. Alum flocculation of
high rate pond water, and recovery and reuse of the recovered aluminium was conducted
over ten cycles in duplicate and compared to a control series in which only fresh alum
was used for flocculation and recovered aluminium was not recycled. Tests continued
over ten days, one cycle per day, to reveal influences of any variations in pond
characteristics resulting from climatic changes. The aluminium mass balance curves are
shown in Fig. 6. Although variations in recoveries were observed, differences between
recycled alum and the control were not proven to be significant (p = 0.05). The average
recovery for the control was 74% and that for the recycled duplicates was 75% indicating
that the percentage of aluminium recovered was not affected by its continued reuse. No
significant reduction in flocculating capacity of the recycled alum was observed.
THE ALGAE BYPRODUCT
The algae byproduct may be a marketable commodity, the sale of which could be used
to offset sewage treatment costs. In order to estimate the value of algae it is necessary to
determine its potential market profile.
Algae (Chlorella) are being commercially produced in Japan and Taiwan*.
* Nihon Chlorella Co. Ltd., Kunitachi-shi 1796, Tokyo; New Sunpack Co., 13-7, 4 Chome, Ginza,
Chuo-ku, Tokyo; and Chlorella Industry Co., Ltd., 4-3, Shiba-Hamamatsu-cho, Minato-ku, Tokyo.
527
aluminium from the algae slurry would reduce overall coagulant requirements as the
aluminium could be recycled and reused as a primary flocculant. Aluminium remaining in
the algae has been shown to be toxic to chickens ingesting the product at 6% dietary
levels (Rachapaetyakom and McGarry, 1971). It was therefore considered desirable to
remove aluminium from the product.
Aluminium extraction by acidification was investigated (Fig. 5). This technique has
been used in water treatment practice (Roberts and Roddy, 1960). Methods used in our
laboratory comprised pond water flocculation and settling in 6-litre jars, algal slurry
separation by supernatant decantation, acidification using sulphuric acid and alum
recovery by vacuum filtration.
Preliminary tests revealed that the appropriate pH range during acidification for
recovery was pH 3 to 4.5. Within this range aluminium recovery varied between 1 l%and
71% (Fig. 6). Physical damage to the algal cells was observed at pH levels below 3. Some
aluminium was lost in the supernatant, much of it in the form of visible unsettled floes.
These could be recovered at the prototype plant scale by dual media filtration. For the
purpose of these studies the aluminium lost with the supernatant was considered as a loss
from the system. pH 3.6 was chosen as the optimum pH in view of algal product quality
and economics of recovery.
After entering the continuous recycle system some of the aluminium is lost to the
flotation units underflow, and some to the algal product; the remainder is recycled.
Aluminium losses from the system continue with subsequent recycles. After many cycles,
very little of the original aluminium remains within the system. The fraction of original
aluminium remaining after n recycles may be estimated as Y n = R
n , where R is the
fraction recovered by acidification. The average number of passes which aluminium
makes through the system is 1/(1—R). Thus if 70% recovery is achieved only 0.3% of the
original aluminium would remain in the system after ten recycles, the average number of
recycles being 3.3 for such a system.
In order to study recovery and flocculating characteristics of recovered aluminium the
continuous recycle process was simulated by semi-batch technique. Alum flocculation of
high rate pond water, and recovery and reuse of the recovered aluminium was conducted
over ten cycles in duplicate and compared to a control series in which only fresh alum
was used for flocculation and recovered aluminium was not recycled. Tests continued
over ten days, one cycle per day, to reveal influences of any variations in pond
characteristics resulting from climatic changes. The aluminium mass balance curves are
shown in Fig. 6. Although variations in recoveries were observed, differences between
recycled alum and the control were not proven to be significant (p = 0.05). The average
recovery for the control was 74% and that for the recycled duplicates was 75% indicating
that the percentage of aluminium recovered was not affected by its continued reuse. No
significant reduction in flocculating capacity of the recycled alum was observed.
THE ALGAE BYPRODUCT
The algae byproduct may be a marketable commodity, the sale of which could be used
to offset sewage treatment costs. In order to estimate the value of algae it is necessary to
determine its potential market profile.
Algae (Chlorella) are being commercially produced in Japan and Taiwan*.
* Nihon Chlorella Co. Ltd., Kunitachi-shi 1796, Tokyo; New Sunpack Co., 13-7, 4 Chome, Ginza,
Chuo-ku, Tokyo; and Chlorella Industry Co., Ltd., 4-3, Shiba-Hamamatsu-cho, Minato-ku, Tokyo.