The Effects of Sewage Treatment Works on Watercourses - T.Swain
Konnaris - CEG8110
1. PHOSPHORUS REMOVAL AND GENERAL
PERFORMANCE ASSESSMENT OF
DOWN-FLOW HANGING SPONGE (DHS)
REACTORS AS A SECONDARY
TREATMENT PROCESS FOR THE
TREATMENT OF DOMESTIC WASTEWATER
STUDENT: ALEXANDROS KONNARIS
SUPERVISOR: PROF. DAVID GRAHAM
DATE: 2ND SEPTEMBER 2016
3. Introduction
Reusing water is vital in conserving it, as well as minimizing
its waste.
Down-flow hanging sponge (DHS) reactors offer the
option of a low-energy biological system treating
wastewater, which can be applied to decentralised
water supply systems.
The 91/271/EEC Urban Waste Water Treatment Directive
(EEC Council, 1991), UWWTD in short, provides the
regulatory guidelines for the quality of treated waters,
against which the results of the study were compared to
assess its performance and compliance.
4. Background
Decentralised water supply and low energy treatment
techniques are very important for developing countries who do
not possess the funds for advanced technologies and well
planned water supply networks.
DHS reactors in the past were used as tertiary treatment units,
usually treating effluent from Up-flow Activated Sludge Blanket
(UASB) reactors.
The DHS performance results in the past showed good potential
for the use of this method as a secondary treatment technique.
5. Aim
To assess the performance of two DHS reactors as secondary process units in treating
domestic wastewater, focusing on its effectiveness in removing phosphorus from the influent.
Objectives:
In phase 1, achieve reactor acclimation.
In phase 2, test the purification efficiency for settled domestic wastewater from a
municipal water treatment plant and its compliance with the UWWTD 91/271/EEC.
If requirements are not met, modify the reactors and repeat the process of phase 2.
Test the hypotheses of: - Alternating oxygen regimes achieving phosphorus removal.
- Reactor 2 design is to be more effective than Reactor 1.
- The large Hydraulic Retention Time (HRT) will bring better results.
6. Methodology
- Activated sludge and wastewater were circulated in the reactors
during phase 1.
- Standard methods were used for the sample analyses, for:
- Total and Volatile Suspended Solids (TSS and VSS)
- Ammonium (NH4-N)
- Total Kjeldahl Nitrogen (TKN)
- Chemical Oxygen Demand (COD)
- Total Dissolved Phosphorus (TDP)
- Dissolved Oxygen (DO)
- Alkalinity
- Bacteria Enumeration
- pH
- VFA
7. Design
HRT was calculated to be 93 hours.
In the anaerobic regions poly-
phosphate is used up by organisms
as energy, releasing phosphorus as
orthophosphate and taking up
carbon.
In the aerobic regions, carbon is
oxidised to carbon dioxide,
releasing energy and allowing
Phosphorus Accumulating
Organisms (PAO) to uptake the
free orthophosphate.
11. Design Modifications
Some of the
sponges in section C
were replaced with
a layer of Granular
Activated Carbon
(GAC).
The changes were
identical for the two
reactors.
14. General Results
Date Reactor 1 Reactor 2
06-Jun 99.98 99.99
20-Jun 99.99 99.99
24-Jun 100.00 99.99
08-Jul 99.73 99.66
15-Jul 99.95 99.78
22-Jul 99.99 99.85
Removal rates of Total Coliforms during phases 2 (light blue) and 3 (red).
Total VFA to Total Alkalinity ratio was on average 1.976 and 0.355 for reactors
1 and 2 respectively, where values greater than 1 show poor reactor stability.
15. Summary of Results Parameter
UWWTD
Limit / Min
reduction
Reactor 1 Reactor 2
Phase 2 Phase 3 Phase 2 Phase 3
COD concentration 125 mg/L 37.5 mg/L 28.9 mg/L 46.9 mg/L 26 mg/L
COD removal rate 75 % 89.5 % 90.5 % 86.9 % 91.4 %
Total Nitrogen
concentration
10 mg/L 16.4 mg/L 11.7 mg/L 11.8 mg/L 5.1 mg/L
Total Nitrogen
removal rate
70-80 % 64.1 % 69.5 % 75.3 % 85.2 %
TDP concentration 1 mg/L 4.4 mg/L
2.7 mg/L
(Min: 1.95 mg/L)
3.6 mg/L
2.6 mg/L
(Min: 2.3 mg/L)
TDP removal rate 80 % -20.7 %
36.4 %
(Max: 54.2 %)
-2.2 %
38.8 %
(Max: 54.2 %)
Solids concentration 35 mg/L 7.5 mg/L 6.8 mg/L 5.7 mg/L 5.5 mg/L
Solids removal rate 90 % 93 % 94.9 % 94.6 % 92.8 %
Reactor 2 was found to
be superior to reactor 1
throughout phase 3
Reactor 2 was also
better than reactor 1
during phase 2, with the
exception of COD
removal
16. Conclusions
Reactor 2 design was proven to be more effective than
Reactor 1 in all parameter comparisons.
Neither the alternating oxygen regimes, nor the very long
HRT presented any potential in removing phosphorus.
The GAC technique managed to achieve significant
phosphorus reduction, yet it had a short lifetime.
The growth of PAO proved to be harder than expected.
Further research on other absorbing material and on
PAO growth could be useful in improving DHS reactors.
