Primary Waste Water Treatment with Septic Tank
>95% of raw sewage is water, most of pollutants can be removed with a septic tank
Heavier fractions sink to the bottom and are decomposed by bacterial interaction > SLUDGE
Lighter fractions such as oil, plastics, surfactants are trapped between baffles > SCUM
 Scum & Sludge need to be evacuated periodically to sustain the septic tank effectiveness
 Rainwater should not be fed to into septic tanks since it can flush scum and sludge into
the drainage gutters and out fall systems
Tank sealing: Sikadur http://www.sika.com.ph/sikadur__31_cf_normal.pdf
Working hypothesis: DENR standards for deep sea discharge can be
met, especially when the drainage system handles rainwater, septic
tank effluents and sea water infiltration together, allowing for sufficient
dilution prior to release to the ocean.
Bounds, T.R., “ Design and Performance of Septic Tanks,”
“Current septic tank technologies are
capable of treating wastewater (onsite)
to a higher level of quality than do
the vast majority of municipal treatment
plants. Properly designed, these onsite
technologies are more fail safe
and fail soft than municipal facilities.
Effluent sewer and onsite wastewater
technologies have been established as
an affordable and reliable
alternative. Passive—energy free—
septic tanks provide the most cost
efficient method of primary treatment
available for nonindustrial sewage.”
Tautology:
“In theory any
effluent could be
diluted with sea
water until it
would meet DENR
standards before
being discharged
to the ocean”
http://www.csuchico.edu/cwtrc/PDFFILES/Updates/Boundsseptictank.pdf
CONCEPT DEEP SEA OUT FALL
desinfect
SEPTIC
TANK
deair
Collection Tank +10m ASL
rain water
Pump-out
Surge tank
beach
shore line
costal water = <3 km or <200m BSL
CT
Sabang
st
st
st
st
st
Small LaLaguna
st
beach
st = surge tank with sump pump
ct = collection tank
deep sea out fall
beach
Big LaLaguna
st
st
beach
= new installation
rain gutter
beach-front path
Septic
tank
gutter, sewerage
surge tank &
sump pump
beach
shorefront effluent HDPE collection pipe
buried in beach
HDPE pipe jointed by
butt welding and
thermoplastic coupling
for pressure rating
of min 3 bar (30m head)
Sump pump operation during brown out utilizing existing private backup
generators (instead of deploying a dedicated backup power system)
grid power
ATS
meter
Private resort/hotel
with backup generator
charges Barangay for
sump pump power
consumption
GENSET
soft starter
sump pump - 1KW
resort/hotel
Max. 3500 m3/day = 40 liter/sec = 150,000 liter / hr (PEMSEA assumption -- for validation)
Collection tank for de-airation and desinfection: 20 m3
1m
Collection Tank
(approx 15m above high tide level)
2m
10m
Sump pump with 15 m head and 40 liter/ sec capacity has a power requirement
of approx. 16 * 15 * 40 = 9,6 KW .
Distributed to 10 surge tanks along the beaches
that’d be 10 sump pumps with 1 KW rating each on average.
The genset backup thus should have a rating of at least 15 KW,
provided the sump pumps are fitted with soft starters.
Pumps will only operate in unison during heavy rain, otherwise
intermittently whenever the surge tank fill level so requires.
Out Fall with .55 m/s flow to convey +40 liters/sec would
need a diameter of 1 ft. Depending on length of out fall, head and
suction a out fall point, a lesser diameter of 1 ft may be viable.
Head to over come pipe pressure drop (@ 2km length) = ~ 2,3 m
Head to overcome density delta 1.026 * depth of 100m = ~ 2,6 m
http://www.pressure-drop.com/
sump pump (generic)
Securing out fall pipe to the sea bead
Options:
- bury in the near foreshore
- weigh down with stones
- “nail” down with augers
- utilize wreck material
- attract coral growth
new coral growth
nylon tie
stone
auger
Diffuser Concept with Suction Effect
Note: ocean water has
higher density than waste
water. The delta determines
how high the feed-in point
has to be above sea level
for the waste water to flow
through the out fall pipe by
gravity alone. The deeper
the discharge point below
sea level the higher the
feed-in point above sea
level.
If waste water contains
bubbles the water column in
the out fall may “float”, thus
flow would stop. Essential
then to allow waste water to
de-air in the collection tank.
suction and diffusion cone
prevailing currents
waste water out fall
anchored on ocean bed
Flow resistance of pipe
(smooth bore or spiral) adds
to required head to achieve
flow requirements.
flexible hose
waste water extraction by ocean current
- reduces head
- regulates outflow according to current
- contains initial mixing zone in cone
- avoids siltation of outlet vents
- reduces risk of out fall flotation
“Septic tank performance can be maintained by
periodically evacuating accumulated scum & sludge”
Cost of sewage evacuation truck: “under 1 mio Pesos”
Bill of Materials –preliminary estimate
Item
Unit
Quantity Unit Cost
Total Cost
beach front
collection pipe
m
1500
1,000
1,500,000
surge tanks
4m3
10
20,000
200,000
sump pumps
1kw
10
30,000
300,000
collection tank
20m3
1
80,000
80,000
out fall pipe
1ft dia
m
2000
1,000
desinfector
1
1
50,000
50,000
electricals
1 lot
1
200,000
200,000
fittings, etc.
1 lot
1
200,000
200,000
genset, ATS
1 lot
1
400,000
400,000
labor
1
1
2,000,000
1,000,000
5,930,000