Name: CG Constructed Wetlands™
Brand: Critical GREEN

Overview

CG Constructed Wetlands™ encompass four types of nature-based treatment systems: Horizontal Sub-Surface Flow (HSSF), Vertical Flow (VF), Free Water Surface (FWS), and Floating Treatment Wetlands (FTW). These systems harness plants, media, and microbial communities to achieve effective BOD, TSS, nutrient, and pathogen removal with minimal energy. They can be designed as standalone systems or combined in hybrid treatment trains. Particularly valuable for housing societies, rural municipalities, sugar mill polishing, and agricultural reuse where land is available, energy cost is a concern, and long-term low-maintenance operation is a priority.

Screen→ ABR/Primary Settling→ HSSF or VF Wetland→ FWS Polish→ Irrigation Reuse

Working Principle

In HSSF wetlands, pre-treated wastewater flows horizontally through a gravel-filled bed planted with emergent aquatic plants (typically Phragmites australis — common reed). Anoxic microbial communities degrade organic matter and denitrify nitrogen. In VF wetlands, wastewater is intermittently loaded on the surface and percolates vertically through layered sand and gravel, creating aerobic conditions enabling nitrification. FWS wetlands channel wastewater as open flow through shallow basins with aquatic plants. FTW systems deploy buoyant modular planting rafts on existing water bodies, suspending plant roots directly into the water column.

Key Technical Features

Four system types: HSSF, Vertical Flow, FWS, Floating (FTW)
HSSF: zero energy, subsurface — no odour, no mosquito habitat
VF: intermittent loading — nitrification capability
FWS: open water, aquatic habitat, tertiary polishing
FTW: retrofit to existing ponds and lakes
BOD removal: 70–95% depending on configuration
Combined nitrification (VF) + denitrification (HSSF) available
Pathogen removal without chemical disinfection
25–30 year design life
Gravity operation — zero energy for HSSF and FWS
Creates landscape amenity and biodiversity habitat
Phragmites australis, Typha, and native wetland species

Design Parameters

Parameter	Value
Types	HSSF/VF/FWS/FTW
Flow Range	20–5,000 m³/day
BOD Removal	70–95%
NH₃-N Removal	60–90% (VF stage)
HRT	2–7 days HSSF
Media	Gravel 20–40 mm HSSF
Design Life	25–30 years
Energy	Zero to Minimal

Applications

Municipal sewage polishing after ABR or primary settling
Sugar mill effluent polishing
Housing society sewage treatment (ABR+HSSF combination)
Agricultural reuse — treated effluent for irrigation
Hospital and institutional sewage treatment
Stormwater management and phytoremediation
Rehabilitation of contaminated ponds (FTW)
Hotel and resort wastewater with landscape integration

Advantages

Zero or minimal energy cost — lowest lifecycle operating cost
No mechanical equipment to maintain in HSSF/FWS
Creates green landscape and biodiversity value
25–30 year lifespan with minimal maintenance
No chemicals required for treatment
Natural carbon sequestration by wetland plants
Suitable for communities with limited technical capacity
Phytoremediation of heavy metals and micropollutants

Frequently Asked Questions

How much land does a constructed wetland require? +

HSSF wetlands typically require 2–5 m² per person served. For a 500-person housing society generating 100 m³/day, an HSSF wetland of approximately 600–1,500 m² is needed. VF wetlands are more compact at 1–2 m²/person.

Can constructed wetlands work in Pakistan climate? +

Yes — constructed wetlands perform very well in Pakistan's climate. Warm temperatures (25–40°C) enhance biological activity year-round. HSSF systems treat effectively even in cooler months due to insulation by the gravel cover. Phragmites australis grows vigorously in Pakistani conditions and is available locally.

Do constructed wetlands produce odours? +

HSSF and VF wetlands do not produce odours as wastewater is contained below the gravel surface. All CG designs include appropriate pre-treatment (ABR or primary settling) to prevent overloading and odour production.

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System Types

Wetland Configurations

HSSF — Horizontal Sub-Surface Flow

In HSSF systems, wastewater flows horizontally through a gravel or crushed-rock substrate below the surface. Treatment occurs through microbial activity in the gravel bed and in the root zone of the macrophytes.

Primary biological treatment — BOD and TSS removal
Substrate: 5–10 mm washed gravel, 60–80 cm depth
Plants: Phragmites australis (common reed), Typha sp.
HLR: typically 50–100 mm/day
No surface water — low odour, low insect risk
Proven in Pakistan: sugar mills, housing societies, institutional

When to use: Best for secondary/tertiary polishing after pre-treatment (septic tank, ABR or primary clarifier).