Wastewater as a resource Strategies to recover resources from Amsterdam’s wastewater

17 Resources are becoming scarce. Therefore, reuse of resources is becoming more and more attractive. 18 Wastewater can be used as a resource, since it contains many resources like organic matter, 19 phosphorus, nitrogen, heavy metals, thermal energy, etc. This study focused on the reuse of organic 20 matter and phosphorus from Amsterdam’s wastewater. There is a wide variety of possible 21 alternatives, and the technical options are growing. The problem is not the availability of technology 22 for resource recovery, but the lack of a planning and design methodology to identify and deploy the 23 most sustainable solutions in a given context. To explore alternative, coherent and viable strategies 24 regarding resource recovery from Amsterdam’s wastewater chain, the development process of 25 dynamic adaptive policy pathways was used. In the first phase a material flow analysis was made for 26 Amsterdam’s wastewater chain and analyzed for water, organic matter and phosphorus. In the 27 second phase measures were identified and characterized. The characterization was based on criteria 28 focusing on changes in material flows, recovered products and implementation horizon. For the 29 Amsterdam case recovered products concerned alginic acid, bioplastic, cellulose, phosphorus and 30 biogas. In the third phase the measures possibilities and uncertainties. It resulted in a coherent policy as the resource recovery goals became 36 clear, a flexible policy as the lock-in, no-regret and win-win measures could be identified, and an up- 37 to-date policy as a periodic update is possible that will reveal new chances and risks.

for resource recovery, but the lack of a planning and design methodology to identify and deploy the 23 most sustainable solutions in a given context. To explore alternative, coherent and viable strategies 24 regarding resource recovery from Amsterdam's wastewater chain, the development process of 25 dynamic adaptive policy pathways was used. In the first phase a material flow analysis was made for 26 Amsterdam's wastewater chain and analyzed for water, organic matter and phosphorus. In the 27 second phase measures were identified and characterized. The characterization was based on criteria 28 focusing on changes in material flows, recovered products and implementation horizon. For the 29 Amsterdam case recovered products concerned alginic acid, bioplastic, cellulose, phosphorus and 30 biogas. In the third phase the measures were combined into strategies, which are combinations of 31 measures that focus on a specific goal of resource recovery. For the Amsterdam case this resulted in 32 four strategies: a strategy focusing on production of alginic acid, a strategy focusing on production of 33 bioplastics, a strategy focusing on recovery of cellulose, and a strategy focusing on recovery of 34 phosphorus. Adaptive policymaking showed to be a good approach to deal with the wide variety of recuperation and production of energy at sewage works is currently getting most attention, the 71 resource recovery from wastewater and sludge should not be overlooked (Van Loosdrecht and 72 Brdjanovic, 2014). 73 The importance to see wastewater as a resource is clear, but the question is where to focus on. 74 There is a wide variety of possible alternatives, as the array of technical options grows. While water, 75 energy and nutrient recovery (phosphorus and nitrogen) are known alternatives ( Van Loosdrecht, 2007) and protein (Matassa et al., 2015). The primary problem is not the availability 80 of technology for resource recovery, but the lack of a social-technological planning and design 81 methodology to identify and deploy the most sustainable solution in a given geographic and cultural 82 context (Guest et al., 2009). According to Li et al. (2015) uncertainties about which techniques are 83 most useful and how to combine them stands in the way of creating 'wastewater-resource factories '. 84 Waternet, the water utility of Amsterdam and surroundings, struggles with this problem. 85 86 Waternet is responsible for the water management in and around Amsterdam. The activities of 87 Waternet concern drinking water supply, sewerage, wastewater treatment, surface water 88 management, control of the canals in Amsterdam and flood protection. The City of Amsterdam, one 89 of two owners of Waternet, has formulated the ambition to develop further as the core city of an 90 internationally competitive and sustainable European Metropolis (City of Amsterdam, 2010). 91 Recently this ambition has been specified in the policy documents 'The Circular Metropolis 92 Amsterdam 2014 -2018' (City of Amsterdam, 2014a) and 'The Sustainability Agenda Amsterdam' 93 (City of Amsterdam, 2014b). In these documents a choice is made for the Circular City concept as a 94 way to achieve the ambition of Amsterdam to develop as a competitive and sustainable European 95 Metropolis. Recovery of resources and materials is one of the main targets and operationalized in 96 the roadmap 'Amsterdam Circular' (Circle Economy et al., 2015). The City of Amsterdam emphasizes 97 that the transition towards a circular city is a shared quest for all stakeholders: companies, city 98 government, inhabitants, research institutes and the financial sector. In this transition phase there is 99 no clear market and thus no clear role for the city government as market regulator. The city 100 government wants to play as a 'game changer' and facilitates involved stakeholders and tries to 101 catalyze promising initiatives (City of Amsterdam, 2014a). As shown in the introduction, the development of coherent strategies to recover resources from 144 Amsterdam's wastewater is characterized by a wide variety of possible alternatives and many 145 external factors, which may change over time due to technological, environmental, economic and 146 market developments. A variety of relevant uncertainties and a variety of possible actions and 147 measures thus impede this development process. There is no fixed policy or strategy, but yet 148 decisions have to be made to achieve the goal of resource recovery from wastewater. Taking into 149 account the similarities between the characteristics of the challenge to develop strategies to recover 150 resources from Amsterdam's wastewater, and the characteristics of adaptive policy making, the 151 research method applied roughly follows the development process of dynamic adaptive policy 152 pathways as described by Haasnoot et al. (2013). 153 The development process as described by Haasnoot et al. (2013) is divided into ten steps, of which in 154 this research only the first six are conducted. Phase A comprises steps 1 and 2, and focuses on the description and analysis of the current situation 161 and perceived problems. As the focus is on materials and material flows in the wastewater chain of 162 Amsterdam, Material Flow Analysis (MFA) was used as tool in phase A. MFA describes and quantifies 163 the material flows through a defined system (Chevre et al., 2013). Since MFA is an indispensable first 164 step for creating a system with increased resource efficiency and reduced losses  Marquet, 2013) and since quantification of the pathway of substances through the socioeconomic 166 system is essential for the selection of appropriate measures to mitigate discharge of this substance 167 (Yuan et   When can the measure be implemented in Amsterdam? 193 Because some measures are competing, it is necessary to know which measures or recovered 194 products are preferred over others. In this research the biomass value pyramid, shown in Figure 2 measures, and makes choices between these, to realize the vision (Rampersad, 2002). In this case the 203 vison of Waternet is to recover resources from Amsterdam's wastewater in order to contribute to 204 the ambition of the City of Amsterdam to make the transition to a circular city. In this research 205 strategies were defined as combinations of measures (derived from phase B) which focus on a 206 specific goal of resource recovery. It was decided that each strategy had to aim at the maximization 207 of a specific product. These products were selected based on experiences at Waternet or research at 208 Waternet (see section 2.2.3) . Cohesion within a strategy was guaranteed by choosing this main focus 209 and making sure that all measures in the strategy corresponded with that focus. Each strategy aimed 210 at maximizing the recovery of one product. When measures, not part of a specific strategy, did not 211 compete with the main goal of this specific strategy, they could also be part of this strategy to 212 recover other resources in the wastewater stream according to the priorities in the value pyramid. 213 The strategies were assessed by use of a strategy diagram. A strategy diagram shows the 214 composition of each strategy and describes how each measure contributes to the strategy. This 215 assessment enabled the identification of lock-ins, win-win situations and no-regret measures. Lock-216 ins are situations when by choosing one measure the option of implementing another measure is 217 eliminated. A win-win situation can exist when a measure is beneficial for two goals. Finally, a no-218 regret measure is a measure that can be implemented in several strategies, so a strategic choice is 219 not yet necessary; the measure is beneficial anyway. 220  Only organic matter and phosphorus were considered. Organic matter was chosen because 233 of the many products that can be made from the organic matter in wastewater. These 234 products all have pros and cons that make recovery more or less financially feasible, 235 technically feasible, sustainable and circular. Also, since these products have the same 236 organic matter as source, they are competing. Therefore, an assessment of products and 237 recovery methods is an important step for the determination of future strategies and

Selected measures 275
In total 21 measures were selected that change the material flows in Amsterdam's wastewater chain. 276 They change the available amounts of resources and/or change how much of these resources can be 277 recovered. The measures can take place at four different locations in the wastewater chain. The first location is the level of the water user: the households and businesses. The second location is the 279 collection of wastewater or the sewer system. The third location is the WWTP and the fourth location 280 is the sludge disposal. Table 1

Selected products 287
Five different products were considered that can be recovered from the wastewater. Table 2

Criteria 298
The measures were characterized using nine criteria, as shown in Table 3. These criteria focused on 299 changes in material flows, recovered products and implementation horizons: the criteria describe 300 how a measure changes material flows (water, organic matter and phosphorus: criteria 1-3) and 301 resource recovery (organic matter and phosphorus: criteria 4-5), what the value of recovered 302 products is (criterion 6), how uncertain a measure's development path is (criterion 7), how the 303 measure depends on changes of behavior or actors outside Waternet (criterion 8) and when it can be 304 expected to be implemented in Amsterdam (criterion 9). 305 and restaurants, and 4.3 million m 3 is used in industry. It is assumed that approximately 2.5% of the 314 water which is distributed to households and business is consumed and therefore is removed from 315 the water chain. An example of water consumption is water that evaporates and is 'lost' to the 316 atmosphere. The remaining 97.5% of the distributed water is used, but returns to the water chain 317 and together with storm water and infiltrated ground water is transported via sewers to wastewater 318 treatment plants (WWTPs). The total wastewater flow is 74.9 million m 3 /year. 319 At WWTP Amsterdam West sludge is currently treated using a mesophilic digester. After part of the 329 water in the sludge has been removed the sludge is digested producing biogas. Most of the biogas is 330 used for combined heat and power production. Part of the biogas cannot be used or stored directly 331 and is therefore lost as gas flare. In 2013 gas flare was around 3% of the total biogas production. The 332 rest of the biogas was upgraded to green gas, which has a higher methane content than biogas and 333 can therefore be used as a transportation fuel. 334 Not all organic matter becomes biogas. The majority of the organic matter is not digested and 335 remains in the sludge. After digestion the sludge is incinerated at the waste and energy company 336 AEB, which is located adjacent to WWTP Amsterdam West. The residual heat of this incineration is 337 used for district heating. 338 Figure 6 shows the phosphorus in Amsterdam's wastewater. It is unknown how much of the 339 phosphorus load at WWTPs originates from households and how much originates from businesses. 340 Therefore, the assumption was made that the composition of household wastewater is comparable 341 with the composition of business wastewater. Since small businesses, which make up more than 70% 342 of businesses' water use, are mostly offices and hotels and catering industry, this assumption seems  (Table 1) were evaluated based on the nine criteria (Table 3). Supplementary 354 Material 2 shows this evaluation in detail. 355 356 All measures influence water, organic matter and/or material flows (criteria 1-3). Thereby, they 357 change the resources that are or can be recovered. An example is the measure of green waste 358 disposals. These grinded green household wastes enable transportation of this organic matter using 359 sewers. The extra organic matter arriving at the WWTP can be recovered using existing technology 360 (e.g. mesophilic digestion) or new technology (e.g. fermentation to produce bioplastic). Water use of 361 households will also increase when people start using these waste disposals. So, measures can 362 change material flows and, thereby, change the amounts of potentially recovered products. The value of the five recovered products (criterion 6) was ranked using the value pyramid (Figure 2). 377 Products higher in the value pyramid are valued higher and therefore preferred over products lower 378 in the pyramid. Biogas was ranked at level 2 (transportation fuels) as it may be converted into Green 379 Gas and used as transportation fuel (Van der Hoek, 2012b ). Cellulose, bioplastics, phosphorus and 380 alginic acid were ranked at level 3 (materials & chemicals), while their value increased in this order in 381 level three. Cellulose is the polysaccharide of which the fibers in toilet paper consist. The fibers can be used to produce building materials and paper products and, therefore, cellulose is placed at level 383 3, materials & chemicals. Cellulose is valued lower than bioplastic, phosphorus and alginic acid, 384 because those three other products have closer links to level 4 (food) and 5 (health and lifestyle). 385 Also traditional production of cellulose (production not from wastewater) is a renewable process, 386 since cellulose is traditionally produced from wood. Because bioplastic is also a material, it is also 387 placed at level 3. Like cellulose, bioplastic also has no close links to food and health and lifestyle. 388 However, because the traditional resources for plastic are fossil fuels, bioplastic is valued higher than 389 cellulose. Since fossil fuel stocks are decreasing, traditional oil based plastic production is not 390 assessed sustainable. The nutrient phosphorus is a chemical and therefore, belongs at level 3. As 391 phosphorus is necessary for food production (level 4) it is valued higher than cellulose and bioplastic. 392 Furthermore, phosphorus stocks are decreasing and, therefore, alternative, more sustainable stocks 393 are desirable. Finally, alginic acid is valued highest. This polysaccharide can be used in the 394 pharmaceutical or food industry and it thus has close links with both levels 4 and 5. So, even though 395 alginic acid falls into the third level, it is valued highest within this level. 396 397 Table 4 shows that only a few of the considered measures introduce new products: cellulose, 398 bioplastic (PHA) and alginic acid. Two of the measures, namely cellulose recovery from primary 399 sludge and the fine-mesh sieve, recover cellulose. Since cellulose would otherwise end up in the 400 sludge and would increase biogas production, these two measures decrease the biogas production. 401 Furthermore, the measures also slightly decrease the struvite production from sludge. In the value 402 pyramid cellulose is valued higher than biogas, so it can be argued that cellulose recovering measures 403 have positive impact on the circularity and sustainability of the wastewater chain. 404 Phosphorus is valued higher than cellulose and since cellulose production also (slightly) decreases 405 phosphorus recovery, this could be a reason not to implement cellulose recovering measures. This 406 illustrates that decision makers need to choose how much reduction in biogas and struvite 407 production can be compensated by cellulose production. Of course other arguments, like investment 408 costs, sales revenues, required chemicals, etc., should also be considered, but the recovering 409 performance of measures is certainly an important aspect in this choice. 410 There is only one measure that produces alginic acid. The combination of the Nereda biological 411 treatment method and alginic acid production from the granular sludge can result in 9.5 kton alginic 412 acid. Since alginic acid is an organic compound, the production of biogas from sludge is decreased 413 when alginic acid is removed from the sludge. The extra phosphorus recovery as struvite is a 414 consequence of the Nereda process which removes more phosphorus from the wastewater into 415 sludge. With regard to the value pyramid this measure should definitely be considered, since the 416 production of a higher valued products, alginic acid and struvite, only reduces a lower valued 417 product, biogas. 418 Furthermore, bioplastic production or PHA production also requires organic matter and therefore, 419 the biogas production decreases when this measure is implemented. As was concluded for alginic 420 acid, bioplastic production should be considered since it increases the production of higher valued 421 products at the cost of lower valued products. 422 Finally, the other measures influence the production of recovered products which are at the moment 423 already produced (biogas and phosphorus as struvite). These measures can, for example, be 424 combined with the measures that recover new products to increase the production of these 425 products. 426 427 Besides the resource recovery capacities of measures, also the timing of measures is important when 428 deciding to implement a resource recovery policy. Some measures may not be the best in producing 429 highly valued products, but they may be the best measures that are feasible at this moment in time. 430 Timing and implementation include the criteria development stage of a measure (criterion 7), the 431 dependencies of measures on external actors and situations (criterion 8) and the implementation 432 horizon (criterion 9). In Supplementary Material 2 these are described in detail for all measures. 433 The first factor to consider is the development stage of the measure (criterion 7). In the case of 434 alginic acid production, the development stage of the technology is highly uncertain resulting in high 435 uncertainties in the implementation horizon. At the moment, it is known that alginic acid is present 436 in granular sludge, but how it can be removed from the sludge, at what costs and with what purity is 437 still very uncertain. Therefore, it is not only unclear when the technology will be fully proven, but it is 438 also unclear whether the measure will ever be technically and financially feasible. In some cases, the 439 development of a technology can be reasonably well predicted, but in other cases the timing of the 440 end of development is highly uncertain. Consequently, measures with unpredictable development 441 paths require highly flexible implementation plans. 442 The second factor to consider is how a measure depends on external circumstances and actors 443 (criterion 8). In the case of bioplastic production, for example, large quantities of sludge and fatty 444 acids are required to make the production profitable. Production of bioplastic requires a complex 445 factory that functions best at a bigger scale. Thus, for bioplastic from wastewater to be a success it 446 would be beneficial to have more water authorities also use their sludge to produce bioplastic. Also, 447 the marketing of the product would benefit from a bigger scale. So, for a water authority to 448 implement bioplastic producing measures, it is dependent on other water authorities. Another 449 example of a dependency on external factors is legislation. At the moment, green waste disposal via 450 sewers is illegal in The Netherlands. So, before water authorities can implement green waste 451 disposals changes of legislation and, therefore, the support of politicians are required. 452 The third factor to consider is the implementation horizon, based on the development stage, 453 dependencies, and the implementation horizon of other measures since some measures depend on 454 others for their success. For example, for Nereda it is better not to have a primary settling tank, for 455 alginic acid production Nereda is a prerequisite, phosphorus can only be recovered from sludge ashes 456 when the sludge is incinerated separately, etc. Thus, whether and when a measure can be 457 implemented depends on whether and when another measure is or can be implemented. Continuing 458 the previous examples, this implies that it is unwise to remove the primary settling tank before it is 459 known when the Nereda process is installed, and alginic acid production cannot start before Nereda process for production of alginic acid, since alginic acid is produced from Nereda's granular 480 sludge. On the contrary, other measures work against the aims of a strategy. In the example of alginic 481 acid production: maximum alginic acid production takes place when granular sludge production is 482 highest. Therefore, it is best not to install a primary settling tank or fine-mesh sieves before the 483 Nereda installation. Thus, these measures are marked with an "-". Finally, measures that are optional 484 for a strategy are marked with an "O". These measures have no impact or a small impact on the main goals of the strategy. For example, measures that take place 'downstream' of the production of the 486 focus product are optional. 487

488
To follow the principles of adaptive policymaking, as a tool to develop alternative, coherent and 489 viable strategies regarding resource recovery in Amsterdam's wastewater chain, it is important to 490 know which measures lead to lock-ins and which measures can be considered no-regret or even win-491 win measures. Lock-ins are decisions that limit the number options that is possible after this decision. 492 For example, when one would choose to produce bioplastic from primary sludge, you severely 493 discourage cellulose recovery. So, measures that are mutually exclusive often lead to lock-ins. Lock-494 ins are visible in Table 5 when the labels of a measure differ per strategy. When a measure is 495 significant (X) for one strategy and negative (-) for another, the decision for or against the measure 496 will limit further choices. On the other hand, measures that do not limit the number of options after 497 a decision is made are considered no-regret measures. An example of this is struvite precipitation. 498 This measure can become less effective when more phosphorus is recovered earlier or later in the 499 wastewater treatment process, but it will still have operational benefits that support the decision for 500 its installation. Some measures can also be characterized as win-win measures. These measures are 501 significant for more than one strategy. For example, thermal hydrolysis is (significantly) positive for 502 alginic acid production, phosphorus recovery and biogas production. 503

504
The most striking examples of competing measures, resulting in lock-ins, are alginic acid and 505 bioplastic production. Since maximum alginic acid production requires maximum amounts of organic 506 matter in the wastewater at the secondary treatment stage of a WWTP and maximum bioplastic 507 production requires as much primary sludge as possible, maximum production of alginic acid and 508 maximum production of bioplastic do not go together. However, it is possible to install both 509 measures, when reduced production is acceptable. So, bioplastic and alginic acid production are not 510 completely excluding each other, but other aspects like investment costs and market prices of the 511 products become more important when one of the two measures is already installed and the other is 512 considered. 513 Cellulose recovery is a no-regret measure on the short-term. When the technologies for cellulose 514 recovery from primary sludge or from the influent using a fine-mesh sieve have been perfected, 515 cellulose can be recovered. Even though Table 5 suggests conflicts with alginic acid and bioplastic 516 production, cellulose recovery measures can be implemented if they reach return of investment 517 before the measures that produce alginic acid and bioplastic are fully developed. However, it is 518 advised that the choice between the two cellulose recovery measures is postponed by one or two 519 years because both measures are still under development. Concluding, cellulose recovery measures can be implemented on the short-term, but in the long run the measures are probably removed to 521 produce alginic acid or bioplastic. 522 Another no-regret measure is phosphorus recovery from sludge ashes. Even though this measure is 523 still being developed and not all pros and cons of the measure are known, the measure has the 524 advantage of being at the end of the wastewater treatment process and is therefore not impacting 525 other measures. Furthermore, phosphorus is a finite chemical, so circularity is more important for 526 this product. Besides recovery from sludge ashes, recovery from urine and recovery from digested 527 sludge through struvite precipitation are also encouraged, since recovery from urine has a high 528 efficiency and recovery from digested sludge, using the existing struvite precipitation system, has 529 operational benefits and a pure product. A remark concerning combinations of phosphorus recovery 530 measures is however that some measures require minimum phosphorus concentrations for them to 531 be effective. So, before deciding to implement measures up-to-date information regarding these 532 minimum phosphorus concentrations is needed. 533 The choice for some measures will depend on the other chosen measures. Thermal hydrolysis could 534 be an example of a win-win measure. Thermal hydrolysis might increase the amount of phosphorus 535 that can be recovered by struvite precipitation and is probably also necessary for alginic acid 536 production. Furthermore, thermal hydrolysis increases the production of biogas from sludge, which 537 could be necessary when cellulose is removed from the sludge, which reduces the degradability of 538 the sludge. So, thermal hydrolysis has many advantages for resource recovery, but the choices for 539 other measures determine how effective thermal hydrolysis will be. Thus . To make use of these benefits, first the Dutch Fertilzers Act 591 had to be changed, otherwise the product struvite would not have any market potential. Especially 592 market potential and market competition introduce uncertainties. Bioplastics have to compete with 593 plastics originating from the petrochemical industry, which are available in high amounts at relatively 594 low prizes. Thus, the market potential of bioplastics seems limited at the moment. The expectation 595 for alginic acid is opposite. Alginates are produced from seaweeds, and the availability and costs of 596 alginate seaweeds is beginning to be a concern of alginate producers. Higher costs have been driven 597 by higher energy, chemicals and seaweed costs, reflecting seaweed shortages (Bixler and Porse, 598 2011). These market conditions may favor the production of alginic acid from wastewater. 599 The method of adaptive policy making also enables to update and expand a specific case when new 620 information becomes available, implying that new opportunities can be seized and threats can be 621 spotted early. So, using this method to create a resource recovering policy helps to develop an 622 adaptive policy that functions well in a highly uncertain future. 623  Separation of primary sludge from the influent at WWTPs by settlement due to reduced flow velocities. 9. Bioplastic production Through fermentation (mixed or rich culture) the bioplastic PHA can be produced from (mainly primary) sludge. 10. Cellulose recovery from primary sludge After primary sludge is separated from the influent using a primary settling tank, cellulose is recovered from the sludge. 11. Fine-mesh sieve & cellulose recovery from sievings A fine-mesh sieve is used to separate larger particles, including cellulose fibres, from the influent.
12. modified University of Cape Town process (mUCT) Current biological treatment process that removes phosphorus and organic matter from the water and stores it (partially) in activated flocular sludge.

Nereda
Biological treatment process that removes phosphorus and organic matter from the water and stores it (partially) in granular sludge. 14. Alginic acid production Alginic acid, a polysaccharide, can be produced from granular sludge. 15. Thermal hydrolysis Pre-treatment of sludge using heat and pressure that sterilizes sludge and makes it more biodegradable. Biogas is a mixture of CH 4 and CO 2 that can be used to produce green gas and CO 2 and/or electricity and heat using combined heat and power technology.

Cellulose
Cellulose is the polysaccharide of which the fibers in toilet paper consist. The fibers can be used to produce building materials or paper products, but it can also be used to make bioplastic.

Bioplastic
Polyhydroxyalkanoates (PHAs), a type of bioplastic, can be produced from sludge. Phosphorus Phosphorus is a necessary nutrient for plant and human growth that can be recovered from wastewater.

Alginic acid
Alginic acid is a polysaccharide that can be used in the pharmaceutical or food industry and that can be recovered from granular sludge.