The Full Story
New Product — Now Available in NZ
Kubota KZII
Advanced Secondary
Wastewater Treatment
Japan's most trusted residential wastewater technology. Independently certified, cold-climate proven, and engineered to perform for 30 years and beyond. Now supplied and installed by A Gradient Drainage
91%
BOD Removal Rate
6
Treatment Stages
30yr+
Engineered Design Life
10M+
Units Deployed Globally
Introducing the KZII
World-leading treatment technology for New Zealand homes
A Gradient Drainage is proud to introduce the Kubota KZII, an advanced Moving Bed Biofilm Reactor (MBBR) wastewater treatment unit developed by Kubota Corporation, a name synonymous with water technology since 1890.
The KZII has been independently tested and verified under Japan's Johkasou Framework, the world's most stringent residential wastewater standard. Its performance levels are consistent with Advanced Secondary classification under AS/NZS 1546.3.
Why it matters for New Zealand: cold-temperature performance is a critical requirement here. The KZII is specifically tested at 13°C, a test not required by AS/NZS guidelines. It's built for our climate.
Verified Performance Data
Independently tested. Consistently exceeds AS/NZS limits.
Tested by the Building Centre of Japan under the Johkasou Framework, which is more rigorous than AS/NZS certification, the KZII delivers Advanced Secondary effluent quality under normal, peak, and cold-temperature conditions.
How It Works
Six stages. Zero single points of failure.
Wastewater flows passively through six discrete treatment chambers, each performing a different biological role. The multi-barrier design means no single chamber failure compromises overall performance.
1
Aerobic Filter
Fixed filter plates remove solids. Microorganisms decompose organics.
4
Moving Bed (MBBR)
Fluidised sponge media. Aerobic BOD removal and ammonia nitrification.
2
Sedimentation Separation
Solids and sludge separated and stored. Scum prevented from re-mixing.
5
Contact Aeration
Fixed contact media. Organic decomposition, nitrification, TSS capture.
3
Anaerobic Filter
Static filter decomposes solids. Denitrification of nitrate nitrogen.
6
Sedimentation
Final TSS removal. Clear supernatant separated, solids recycled to Stage 1.
Domestic Models
Three sizes. Every NZ home covered.
The KZII range fills critical gaps in the New Zealand market, from compact units for small homes to large-capacity systems for family properties.
KZII‑5
1–2 Bedrooms · 1,000 L/day
Length 1,580 mm
Width 980 mm
Height 1,860 mm
Weight 150 kg
Total Volume 1.408 m³
BOD Effluent ≤ 20 mg/L
SS Effluent ≤ 15 mg/L
KZII‑7
3 Bedrooms · 1,400 L/day
Length 2,120 mm
Width 980 mm
Height 1,860 mm
Weight 180 kg
Total Volume 1.957 m³
BOD Effluent ≤ 20 mg/L
SS Effluent ≤ 15 mg/L
KZII‑10
4–8 Bedrooms · 2,000 L/day
Length 2,790 mm
Width 1,200 mm
Height 1,880 mm
Weight 200 kg
Total Volume 3.222 m³
BOD Effluent ≤ 20 mg/L
SS Effluent ≤ 15 mg/L
Why the Kubota KZII
Built tougher. Tested harder.
Cold Climate Tested
An 8-week low-temperature load test at 13°C is mandatory under the Johkasou Framework. AS/NZS doesn't require it. The KZII passed, delivering reliable treatment performance through New Zealand winters.
Independently Certified
Evaluated by the Building Centre of Japan under national mandate. Peak load testing is 1.5 times design capacity over 7 days, and hourly flow testing is 25% of daily capacity, both more demanding than AS/NZS requirements.
130 Years of Heritage
Kubota has manufactured water industry products since 1890. The KZII is the product of 40 years and more of Johkasou research. Units installed in Japan in the 1970s are still operating today, which makes a 30-year engineered design life a conservative figure.
Compact & Easy to Install
Lightweight FRP construction (150 to 200 kg) and a small footprint make the KZII simple to install on difficult sites, sloping ground, or tight sections. Gas-tight covers eliminate odour, and the blower is designed to be near-silent.
Multi-Barrier Reliability
Passive gravity flow paths, four separate media filtration stages, aerobic and anaerobic biological treatment, and peak flow buffering all work together. There's no reliance on any single mechanism, so performance stays consistent under variable loads.
Certified Teams Across New Zealand
A Gradient Drainage works with a nationwide network of certified installers and technicians, so you get expert KZII installation and ongoing support wherever your property is located.
Certifications
Certified to the standards that matter most
BCJ
CERT
Building Centre of Japan
Independent national evaluation. BCJ Eval.-JT0031-01. The designated Johkasou evaluation body under Japanese federal mandate.
JIS
JAS
Johkasou Framework
Under Japan's standards, treated effluent of this quality is suitable for direct discharge to open waterways and stormwater systems. In New Zealand, discharge to water or land is set by your regional council's consent conditions, and we help you meet them.
ISO
9001
ISO 9001 & 14001
Mass produced under certified quality management and environmental management systems. Consistent manufacturing to global standards.
AS/NZS
AVD
AS/NZS 1546.3 Advanced
Test results consistent with Advanced Secondary classification. BOD 17 mg/L (limit 20 mg/L). TSS 13 mg/L (limit 20 mg/L).
Kubota Heritage
The most trusted name in Japanese water technology
Japan operates the world's most regulated wastewater industry. Every Johkasou unit is tested annually by the federal government. Effluent must be suitable for waterway discharge, or the unit is replaced. That's the standard the KZII was built to meet, every single year.
​
The Japanese government tests approximately 8 million Johkasou units nationwide. The KZII's design priorities of reliability, cold-climate resilience, and long service life were shaped by that accountability.