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Pressure and flow recovery: Impact and additionality

One of water's clearest efficiency wins, and a gas caveat

One of water's clearest efficiency wins, and a gas caveat What this tab covers The impact and additionality lens: direct emission cuts, side benefits for water and air, and the risk of prolonging the life of a polluting host plant.

The PX is one of the clearest efficiency wins in water. The other variants are small per site, and their climate value depends on the grid they displace and, for gas, on how the preheat is supplied.

Direct Scope 1 and Scope 2 abatement

Mixed

PX devices cut seawater RO energy use by up to 60%, and the plants using ERI devices supply over 43 million m3 a day. In-pipe hydro avoids Scope 2 emissions only in proportion to its small output, for example 150,000 kWh a year at EBMUD. Compressor heat recovery avoids Scope 1 gas burning directly. The 100 bhp example replaces about 10,000 therms of gas a year (calculated from USD 6,975 at USD 0.70 per therm, which already allows for an 85%-efficient heater). A gas expander's net benefit can be close to zero if the preheat is gas-fired.125

SWRO energy cut with PX up to 60%1 EBMUD in-pipe output 150,000 kWh/y from 30 kW5 US conduit hydro 530 MW existing, up to 1.41 GW untapped5

Water and air synergy

Favourable

Lower energy per cubic metre of desalinated water makes desalination less carbon-heavy and cheaper in water-stressed regions such as the Gulf and India's coast. Wastewater variants of the PX target zero liquid discharge, where the source says thermal treatment can be up to 50% of costs. Gas expanders avoid the extra combustion of a preheater only if waste heat or a heat pump supplies the heat.13

Thermal share of ZLD costs up to 50%1

Avoided lock-in

Mixed

Water-side variants carry no fossil lock-in. Gas letdown expanders earn money from fossil gas flow, so they gain from a large gas network and give the owner a small reason to resist shrinking it. The H2Tech study proposes using expander power for on-site electrolysis, which would tie the asset to gas flows for longer.3

Sources

  1. Energy Recovery, Inc. Form 10-K for fiscal year 2025 (company filing) Energy Recovery, Inc. (US SEC filing), 2026
  2. Fact Sheet 10: Heat recovery with compressed air systems (updated 2026) Compressed Air Challenge (sourcebook developed with US DOE), 2026
  3. H2 production through gas pressure utilization at natural gas transmission network stations (G. Vallios, METRON SA) H2Tech, 2023
  4. Water and wastewater systems hydropower guide (document 24-50213) Pacific Northwest National Laboratory and Idaho National Laboratory for US DOE Water Power Technologies Office, 2024