The independent high rate algal pond as a unit operation in tertiary wastewater treatment
- Authors: Clark, Stewart James
- Date: 2002
- Subjects: Algae -- Biotechnology , Sewage -- Purification -- Biological treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4092 , http://hdl.handle.net/10962/d1007805
- Description: The development of the High Rate Algal Pond (HRAP) as an independent tertiary treatment unit operation for phosphate and nitrate removal is reported. A novel Integrated Algal Ponding System (lAPS) design is proposed for nutrient removal from the effluents of both a conventional domestic sewage treatment plant and from an Advanced Integrated Wastewater Ponding System (AIWPS). The viability of an independently operated HRAP has been identified and termed the Independent High Rate Algal Pond (l-HRAP). A 500 m² pilot 1- HRAP was operated in such a way as to facilitate the precipitation of calcium phosphate, known to be controlled by pH (greater than 9.4) and resulting in final phosphate levels of less than 1 mg.L⁻¹ as P0₄-P. The incorporation of the I-HRAP into a denitrification process was also investigated. Continuously fed column reactors, utilising algal biomass as a carbon source, showed that the heterotrophic bacterial community dominant in the anaerobic algal sludge were denitrifying the nitrate in the feed. It was demonstrated that as the cultures were stressed (using increased nitrate concentrations, anaerobiosis and light starvation) total polysaccharide (TPS) concentrations increased, with a notable increase 111 the exopolysaccharide (EPS) fraction. These experiments corroborated the hypothesis that harvested microalgal biomass can be manipulated to produce, and release, exopolymeric substances under stress conditions, and which may serve as carbon source for denitrification. In both batch flask studies and in laboratory-scale reactor systems, harvested microalgal biomass from an HRAP was shown to produce exopolymeric substances under stress conditions. Initial high loading-rates of greater than 20 mg.L⁻¹ NO₃-N resulted in double the amount of exopolysaccharide production than in flasks with initial low loading-rates (less than 5 mg.L⁻¹ NO₃-N). Making use of an upflow anaerobic sludge blanket-type degrading-bed reactor, and an anaerobic, flooded trickle filter (ANTRIC) receiving HRAP effluent, the relationship between denitrification and the changes in polysaccharide content was investigated. This phenomenon has considerable beneficial implications in biological wastewater treatment systems where high nitrate concentration in the final effluent is a potential mitigating factor. Identification of the heterotrophic bacteria active in the denitrification process was attempted. This study presents a first report on the development and operation of the I-HRAP and has been followed by a technical-scale pilot plant evaluation of the process in the tertiary treatment of domestic wastewaters.
- Full Text:
- Date Issued: 2002
Post-treatment technologies for integrated algal pond systems
- Authors: Westensee, Dirk Karl
- Date: 2015
- Subjects: Sewage disposal plants -- South Africa -- Grahamstown , Water -- Purification -- Filtration , Water -- Purification -- Slow sand filtration , Sewage -- Purification -- Anaerobic treatment , Sewage -- Purification -- Biological treatment , Algae -- Biotechnology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5958 , http://hdl.handle.net/10962/d1018180
- Description: Integrated Algae Pond Systems (IAPS) are a derivation of the Oswald designed Algal Integrated Wastewater Pond Systems (AIWPS®) and combine the use of anaerobic and aerobic bioprocesses to effect wastewater treatment. IAPS technology was introduced to South Africa in 1996 and a pilot plant designed and commissioned at the Belmont Valley WWTW in Grahamstown. The system has been in continual use since implementation and affords a secondarily treated water for reclamation according to its design specifications which most closely resemble those of the AIWPS® Advanced Secondary Process developed by Oswald. As a consequence, and as might be expected, while the technology performed well and delivered a final effluent superior to most pond systems deployed in South Africa it was unable to meet The Department of Water Affairs General Standard for nutrient removal and effluent discharge. The work described in this thesis involved the design, construction, and evaluation of several tertiary treatment units (TTU') for incorporation into the IAPS process design. Included were; Maturation Ponds (MP), Slow Sand Filter (SSF) and Rock Filters (RF). Three MP's were constructed in series with a 12 day retention time and operated in parallel with a two-layered SSF and a three-stage RF. Water quality of the effluent emerging from each of these TTU's was monitored over a 10 month period. Significant decreases in the chemical oxygen demand (COD), ammonium-N, phosphate-P, nitrate-N, faecal coliforms (FC) and total coliforms (TC) were achieved by these TTU's. On average, throughout the testing period, water quality was within the statutory limit for discharge to a water course that is not a listed water course, with the exception of the total suspended solids (TSS). The RF was determined as the most suitable TTU for commercial use due to production of a better quality water, smaller footprint, lower construction costs and less maintenance required. From the results of this investigation it is concluded that commercial deployment of IAPS for the treatment of municipal sewage requires the inclusion of a suitable TTU. Furthermore, and based on the findings presented, RF appears most appropriate to ensure that quality of the final effluent meets the standard for discharge.
- Full Text:
- Date Issued: 2015