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Recovery of Wastewater Resources Across Scale

Craig Criddle Civil and Environmental Engineering Woods Institute for the Environment

Stanford University

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Why U.S. Wastewater Treatment Systems Need to Be Rebuilt

  It has reached its design life

 Energy increasingly expensive

  Increased need for nitrogen removal and for removal and recovery of phosphorus

 Water scarcity, drought, and need for security

  Increasing urban populations and need to sustain valuable ecosystems

 Valuable resources are currently wasted

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Water (99.9%) Biodegradable Organics

Nutrients (N and P)

Pathogens Salt

Refractory Organics

Resources

Impurities

Components of Domestic Wastewater

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Resource Per m3 US $

per m3 Organic Soil Conditioner (kg) 0.10 0.03 Methane (m3) 0.14 0.07 Nitrogen (kg) 0.05 0.07 Phosphorus (kg) 0.01 0.01 Water (1 m3) 1.00 0.33

The Value of the Resource

Source: Willy Verstraete (2008)

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Wastewater Treatment Plants Can Become Resource Recovery Centers for Local Markets

 Water Household Business Agriculture

 Organics Energy Materials Animal Feed

 Nutrients Fertilizer Animal Feed

Clean Water Wastewater

Treatment

Waste Carbon

Treatment

Carbon Products (CH4, compost, biochar,

bioplastic, syngas…)

Waste Nitrogen and Phosphorus

Treatment

Nitrogen and Phosphorus Products

(NH3, struvite…)

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At What Scale Should These Resources Be Recovered?

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Scale

  Building: A set of rooms with shared drainage; includes

Hotels Dorms Houses

Stanford Living Innovation Center

(Green Dorm)

  Cluster: A collection of buildings with a shared drainage line for wastewater collection; includes

Small cities HOAs Campuses Farms

Stanford Campus

  Catchment: A region defined by the set of all clusters with a shared drainage system; includes

Cities with a shared treatment facility and shared storm drains Farms with shared drainage

Catchment of the City of Palo Alto

  Watershed: A region defined peripherally by a divide and draining to a particular water body; the set of all catchments within a drainage basin

San Francisco Bay Watershed

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45 billion m3/year

12 billion m3/year

Large Amounts of Energy Are Needed to Pump Freshwater

  From Northern California to Southern California

  From Southern China to Northern China

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Scale

Stanford Living Innovation Center

(Green Dorm)

Stanford Campus

Catchment of the City of Palo Alto

San Francisco Bay Watershed

Energy for Transport of Water to User

High

Low

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 At what scale does resource recovery make sense?

 Which resources should be recovered?

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Approach

 Determine baseline water balances at each scale

 Determine baseline energy audits at each scale

  Identify appropriate technologies at each scale

 Conduct a cost benefit analysis to assess technologies and costs across scale

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Reuse or Receiving Water Body Treatment Plant

Catchment

Buildings at Nodes

Clusters

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Building Scale

Example: Stanford Green Dorm

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Steps used for water balance at the building scale

 Choose time period for balance

 Quantify uses for water plus leaks

 Classify uses according to the required water quality requirement (ex: potable, non-potable)

  Lump together uses of the same quality

 Non-potable supply = sum of non-potable uses + losses + change in storage from previous time period

 Potable supply = total water use – (non-potable water supply + losses) + change in storage from previous time period

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0.01 MG

1.10 MG Indoor

Demand 0.62 MG SFPUC

0.74 MG

0.20 MG

0.6 MG 0.10 MG

0.50 MG

0.10 MG Evapotranspiration

0.04 MG Roof Runoff

0.08 MG Evapotranspiration

0.08 MG Rain

0.04MG Leakage

0.07 MG Landscaping

Water

0.03 MG Pervious Runoff

0.01 MG Evaporation from Roof

0.05 MG Leakage and

Domestic Use

Stormwater

0.01 MG

0.03 MG

0.01 MG

Sewer

Condenser

0.35 MG Blackwater

0.74 MG Greywater

Projected Annual Water Balance

Percentage of Demand Met by Recycled and Collected Water Outdoor: 100% Greenhouse: 100% Indoor: 48% Overall: 58%

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Why Recover Water and Other Resources at the Building Scale?

  It is the point closest to the demand for water; pumping energy will be lowest and pipe length will be shortest

 Dilution of resources in the water will be least; source separation may be possible

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What Technologies Might Make Sense at the Building Scale?

 Greywater treatment and reuse?

 Rainwater harvesting?

 Energy recovery from wastewater (restaurants, dining halls, etc.)?

 Energy recovery from heat in the wastewater?

 Source separation and collection (metals and organics at manufacturing facilities, urine, etc.)?

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Cluster Scale

Example: Stanford Campus

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2.3 0.7 0.5

1.2

Imported

Wastewater

Groundwater Surface Water

1.7

Irrigation and Cooling

Recycled

0.01

Stanford University

Cluster

Potential Resource

Water Balance

Units are m3/d

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Why Recover Resources at the Cluster Scale?

 For many clusters, energy for pumping will be less and pipe lengths will be shorter than from centralized treatment systems

  Recovered water may contain less salt than at centralized facilities

 Sea-level rise could flood some centralized facilities

 Compact systems with remote monitoring now feasible

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What Might Make Sense at the Cluster Scale?

  “Scalping”: Extracting clean water from wastewater for local reuse?

 Energy extraction from organics?

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Ecosystem Restoration

Water Use Aquifer Storage

Cooling

Washing Clothes

Flushing Toilets

Agriculture

Landscape

Salt Removal

Salt to Sewer

Sewer

Residuals to Sewer

Nutrient Removal

Scalping with Distributed Treatment

Residuals to Sewer

Carbon Removal Advanced Oxidation

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Ocean

Treatment Plant

Scalping Facilities

Harvest Water

Scalping Facilities for Water Recovery and Local Reuse

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Critical Technologies at the Cluster Scale

 Highly efficient separators to remove solids

 Reactors for low-energy removal of organics and nitrogen (Goal: net positive energy)

 Advanced oxidation

 Distributed monitoring and control

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Example: Palo Alto Catchment

Palo Alto Treatment Plant

Catchment Scale

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Los Altos Cluster

Mountain View Cluster

Palo Alto Cluster

Stanford Cluster

East Palo Alto Cluster

Los Altos Hill Cluster

Palo Alto Catchment Wastewater Treatment Plant

Imported Water

34 MGD

Groundwater 2.9 MGD

Surface Water 0.5 MGD

Discharge to Bay

24 MGD

Palo Alto Catchment Water Balance

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How Will Water Reuse and Conservation at the Building and Cluster Scale Affect the Catchment Scale?

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Palo Alto

Los Altos

Mountain View

Stanford University

East Palo Alto

Los Altos Hills

Palo Alto Catchment Wastewater Treatment

(Concentrated 2X)

Imported Water 24 MGD

(29%Decrease)

Groundwater 0.3 MGD

(90% Decrease)

Surface Water 0.5 MGD

Discharge to Bay 12.5 MGD

(50% Decrease)

What Happens with 50% Reuse?

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Transport of solids through sewers could be impeded. This has been an “unintended consequence” of water conservation in Southern California.

Sufficient water flow must be provided for water to carry solids or more radical decentralization becomes necessary.

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The Value of the Energy and Nutrients Arriving at the Centralized Facility Becomes Equivalent to That of the Water

x 2 = $0.36 per m3

How Does Resource Value Change at the Treatment Plant If Clusters Reuse 50% of Their Wastewater?

Resource Per m3

US $ per m3

Organic Soil Conditioner (kg) 0.10 0.03

Methane (m3) 0.14 0.07

Nitrogen (kg) 0.05 0.07

Phosphorus (kg) 0.01 0.01

Water (1 m3) 1.00 0.33

Resource Per m3

US $ per m3

Organic Soil Conditioner (kg) 0.20 0.06

Methane (m3) 0.28 0.14

Nitrogen (kg) 0.10 0.14

Phosphorus (kg) 0.02 0.02

Water (1 m3) 1.00 0.33

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Ocean

Treatment Plant

salt

Scalping Facilities

Harvest Water in Clusters

Harvest Water, Energy,

Nutrients in Catchment

Centralized Facilities for Water, Carbon and Nitrogen Recovery

We are currently

developing energy audits for the service area of the City

of Palo Alto

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The Palo Alto Treatment Plant (Built in the 1970s) Uses Large Amounts of Energy

High energy inputs for

incinerator!

Total = 3,300 MJ/1000 m3

198 MJ

396 MJ

429 MJ

132 MJ

132 MJ

66 MJ

1914 MJ

A Typical Wastewater Treatment Plant Uses 1,200–2,400 MJ/1000 m3

33 MJ

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The energy from combustion of the organics in typical domestic wastewater is ~ 6,000 MJ/1000 m3.

So the wastewater contains two to four times more energy than is needed for treatment.

Wastewater treatment could be energy-neutral or even produce energy.

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Advances in Technology Have Improved Recovery of Energy and Other Products

 Organics Energy Materials Animal Feed

 Nutrients Fertilizer Animal Feed

Waste Carbon

Treatment

Carbon Products (CH4, compost, biochar,

bioplastic, syngas…)

Waste Nitrogen and Phosphorus

Treatment

Nitrogen and Phosphorus Products

(NH3, struvite…)

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Example: Nitrogen Removal

  In Europe, full-scale treatment systems that are using a new process for nitrogen removal—“Anammox”—are approaching energy-neutral operation

 The largest Anammox plant in the world (11 tons N/d) is now being designed for the Melhua Group in China (amino acids and starch producer)

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Crystal Green (Struvite)

Example: Phosphorus Recovery

  Mining mineral phosphorus for fertilizer is consuming it faster than geologic cycles can replenish it

  U.S. reserve will last 40 years at current production

  In 2008, China placed a 135% export tariff on phosphate

Process Product Crystalactor CaPO4

PhoStrip CaPO4

Ostara Struvite KREPO Ferric Phosphate Kemicond Ferric Phosphate Seaborne Struvite BioCon H3PO4

SEPHOS CaPO4

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Energy

Dewater

N & P Removal

Microbial Fuel Cell or

Anaerobic Process

Fertilizer

Energy

Energy

Solids

Biosolids

Energy

Energy

Soil Conditioner

Efficient solids

separation

Anaerobic Digester or

Gasifier

Future Resource Recovery Plant?

Fertilizer

Energy

Discharge or reuse

From Sewer

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Internet could enable

coordinated resource

recovery and marketing within

catchments

Information Technology & Remote Monitoring

…and between catchments

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San Francisco Bay

  The San Francisco Bay is protected by 40 treatment wastewater treatment plants

  All are currently involved in master planning to revitalize their wastewater treatment systems

  The effects of regional resource recovery could be dramatic

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The Stanford-Palo Alto Water Team

Frank Josh Tom

Phil

Craig

Marty

Eun Jung

Sebastien

Weimin

David

Sandy

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Support Woods Institute for the Environment, Stanford University City of Palo Alto Stanford Utilities