Process Risk Minimized with Multi-Barrier Clarification

In the past decade the consultant and operations communities have strongly embraced high-rate clarification processes. Relative compact size and rapid response to operational changes are the two main driving forces behind this movement. However, under certain conditions the shortened process residence time can also be a detriment to the processes’ performance. Ancillary equipment failure leads to rapid deterioration in effluent quality. Process chemistry requires careful attention under changing influent water conditions to ensure downstream processes are not adversely affected.

USFilter, part of Siemens Water Technologies, offers the new Trident® HSC clarifier system that provides high-rate clarification in two stages to minimize risk of process failure. The multi-barrier system consists of inclined plate separation with integral sludge recirculation, followed by adsorption clarification. The first stage uses coagulation and flocculation with previously formed solids and polymer to rapidly increase floc settling rate, similar to traditional solids contact reactors. The solids recirculation and contacting process improves operating efficiency while the settled sludge concentrates to reduce waste production.

In the second stage, an Adsorption Clarifier® system uses upflow buoyant media to capture remaining solids. The combination of solids removal methods improves overall clarifier performance. A second polymer addition occurs prior to adsorption clarification to increase floc strength and removal efficiency. Process chemistry is designed to prevent polymer fouling in downstream filtration.

Each stage is operated at approximately twice the standard design rate compared to when used as a stand-alone system.

Surface water clarification for drinking water supply is the largest application for the Trident HSC system. The unit is capable of treating turbidity of 400 NTU and color at 100 units. Total Organic Carbon (TOC) removal exceeding 55% has been demonstrated consistently.

The two-stage clarifier has outperformed single-stage units when enhanced coagulation is used to achieve TOC removal required by the Stage 1 Disinfection By-Products Rule. The multi-barrier treatment system readily satisfies log removal credit requirements for the Long Term 2 Enhanced Surface Water Treatment Rule.

Other Applications

High iron and manganese concentrations in groundwater supplies are another suitable application. Pre-oxidation for floc formation occurs prior to the unit. The same operating principle of increasing contaminant reduction across each stage improves operating efficiency and reduces waste. When elevated arsenic concentrations are present, a co-precipitation reaction with oxidized iron removes both contaminants in one step.

Increasingly, wastewater treatment plants are being required to reduce total phosphorus discharged to minimize algae growth in the receiving water. In some locations, these new limits may be well below 100 parts per billion (ppb). A common phosphorus removal method involves coagulant precipitation like that provided by the Trident HSC system. The system has demonstrated consistent removal to less than 75 ppb total phosphorus using alum or ferric chloride addition. Post-clarifier filtration further improved removal to 10 to 20 ppb effluent concentration.

Trident HSC systems are constructed in concrete tanks for flow rates of 5 mgd and higher. A single inclined plate settler provides pre-treatment to multiple Adsorption Clarifier cells to maintain constant forward flow during Adsorption Clarifier flushing events. When more than one treatment train is required, common wall construction reduces installed cost.

Factory-fabricated tanks of 350 to 1,400 gpm per unit are available for lower flow systems. Pre-engineered packaged units minimize design and installation time.

For more information about the Trident HSC system, visit AWWA Booth 2029 in Hall C or contact Darin St. Germain directly at 515-268-8400 or [email protected].