Sewage Treatment Plant Operation & Maintenance

The aims and objectives of this course are to develop the participants' understanding of the need for effective and efficient operation and maintenance of waste water treatment works. It is proposed to develop this understanding by using a range of visual media to show the participants the range of process units they may encounter. To emphasise how the unit works, a simple explanation of the design criteria may be included, but the main emphasis will be on the operational and maintenance work required to ensure that each process unit works in an effective manner.

The principal approach to the course would be to start on the morning of day one looking at sewerage systems and pumping stations, then logically following the flow of effluent through the process units to the final discharge/disposal points, looking at: the function of each process unit and how its operation affects subsequent units; how the process unit works and simple design criteria; the variations of process unit which may be encountered on a WWTW; process vital sections within a process unit and what preventative maintenance work should routinely be carried out; common errors which can be made in the operation of process units; health safety and environmental issues which should be borne in mind when operating and/or maintaining such process units.

Stage 1 Sewerage Systems & Pumping Stations

Surface water and foul sewerage systems; Combined sewer overflows; Duty/standby/assist pumps & the level control systems; Effects of Hydrogen Sulphide corrosion; Need for confined space protocols & effect of methane, petroleum products, oxygen scavengers etc; Odour control; Lifting and maintenance of pumps.

Stage 2 Preliminary Treatment

Screens Reasons for screen installation; Manual screens versus automatic screens with ultrasonic control; Compactors & skip management; Wash water systems; Effects of grease; Grease removal; Reason for installation of grease removal systems; Principle of operation of grease removal systems; Grit removal; Reason for installation of grit removal systems; Principle of operation of grit removal systems; Grit washing & skip management.

Stage 3 Primary Settlement

Reason for installation of primary settlement and simple design criteria, retention time, hydraulic loading etc; Radial flow , horizontal flow, imhoff tanks and lamella settlers; Importance of effective scum boards and central baffles; Effects of rising sludge; Auto & manual desludging and why it is important that desludging is done correctly.

Stage 4 Biological Treatment

Function of biological treatment stage introducing concepts of BOD, COD & Ammonia.

Filters: Principle of filter process including variations (high rate, plastic & clinker media, SAF & BAF, ADF etc) including simple design principles such as recirculation and wetting rates, hydraulic and organic load; Motor driven distributors, siphon dosing; Routine operational issues such as sparge hole cleaning & rotation mechanism of distributors and air flow through media; Flies & other nuisances.

Activated sludge: Principles of activated sludge treatment systems, including simple design principles such as F/M ratio, RAS, SAS and sludge age; Aeration systems (surface aerators, diffusers etc); Settlement, bulking, nocardia foaming, pin point flocs etc; Anoxic zones, nitrification/denitrification & phosphorous removal; D.O control; Extended aeration, SBR & MBR’s; Simple daily tests such as MLSS, settleability, SSVI , simple microscopic examination; Routine operation and maintenance tasks required on an activated sludge plant.

This section will conclude with a discussion around the advantages and disadvantages of filters and A.S systems.

Stage 5 Secondary Settlement

Reason for installation of secondary settlement and revisiting simple design criteria discussed in primary settlement stage; Radial flow , horizontal flow and lamella settlers; Settlement problems, symptoms effects & solutions; Humus sludge co settlement; Re-emphasis on the importance of correct de-sludging techniques; Daily tasks to be undertaken; Why there is a need to clean channels, weirs, scum boxes etc.

Stage 6 Tertiary Treatment

Why tertiary treatment is needed and typical processes employed including: Reed beds; Grass plots; CSF’s; RGF’s; Lagoons.

Each process will be described along with simple design criteria and daily operational tasks which need to be employed to ensure that such process units work effectively & efficiently.

Stage 7 Auxiliary Units

A “catch all” stage discussing the principles & simple design criteria of process units which do not fit into the above, for example: Wash water units; Odour control systems; Process control, looking at the wide range of control systems which maybe encountered ranging from simple switch systems to complex PC and SCADA controlled systems; Monitoring, looking at the need for representative sampling and the wide range of monitoring devices which may be encountered including flow monitoring, ISE’s , TOC monitors etc.

Stage 8 Sludge

The various sources of sludge the characteristics of different sludges and the effect on these characteristics of mixing or cosettling sludges. The potential routes for sludge disposal will be discussed including the need for treatment before disposal and the advantages & disadvantages of each potential disposal route.

Stage 9 Sludge Thickening

What flocculants & coagulants are how they work & why correct dosing is vital; How to tell by looking at a thickened sludge and the sludge liquor that dosing level is correct (including some simple dosing test techniques , CST etc); Belt presses, centrifuges and filter presses. Including simple design criteria and daily operational tasks which need to be carried out on presses and centrifuges; Effective & correct return of sludge liquors to the works flow.

Stage 10 Sludge Treatment

Mesophilic and thermophillic anaerobic digestion; Lime conditioning; Composting; Fluidised bed Incineration; Vermiculture; Willow coppice treatment

Including a description of how each process works, simple design criteria and the routine operational tasks required with each process.

Stage 11 Health, Safety and Environment

A discussion of the wide ranging risks to health & safety encountered on a waste water treatment works and the precautions which must be taken.