Enhancing anaerobic digestion in urban wastewater management

The thesis investigates how anaerobic digestion could be utilized to improve wastewater management,specifically in regards to future expected regulation on sludge management in Sweden.Two possible paths of applying anaerobic digestion are investigated. First, the usage of thermophilic anaerobicdigestion of sludge in order to achieve pathogen hygienization. Second, the usage of anaerobic digestion totreat wastewaters at decreased temperature. The evaluation of each path was made through practical labscale experiments. Additionally, the benefits of each path was compared through desk top environmentalimpact studies and economic analysis.The results for the first path showed that thermophilic anaerobic digestion renders high pathogen hygienizationeven at relative short exposure times. However no additional beneficial impact on biogas production or thereduction of organic micropollutants was found. The results for the second path showed that the difficulty ofoperating the sensitive anaerobic digestion process at low temperatures can be partly overcome by simpleengineering batch tests. Furthermore, the dissolved methane in the effluent wastewaters can be extractedusing membrane contactors. Finally, the environmental impact assessment showed that increased resourcerecovery from wastewater, as well as decreased climate impact, can be achieved by applying anaerobicdigestion on source separated domestic wastewaster.The economic evaluation of the two paths showed that the implementation of source separation systems isexpensive compared to implementing the needed thermophilic hygienization. However, source separationsystems would greatly boost nutrient recovery from cities to agriculture which complies well with the goals ofthe Swedish Environmental Protection Agency

Evaluating source separation wastewater systems using traditional life cycle assessment and the planetary boundaries approach

Life cycle assessment (LCA) is a commonly used method for assessing environmental impacts of systems, but cannot produce absolute values, i.e. a comparison with existing calculated values, which represents limits of what can be emitted into the environment. Therefore, absolute environmental sustainability assessments have been developed to assess impacts against the planetary boundaries (PBs) of the safe operating space for humanity. Since PB-LCAs are novel, it is useful to analyze both results from this method and conventional LCAs, something which has not been done before. This study applied both methods to two full-scale sanitation systems in the city of Helsingborg, Sweden. The current conventional system for handling wastewater with active sludge and food waste to biogas production was compared with the novel project H+ source separation system with three pipes (food waste, grey and black water) with increased resource recovery through anaerobic digestion, ammonia stripping, struvite precipitation and pelletization. The Planetary Boundaries LCA (PB-LCA) results showed that both systems exceeded eight of the assigned shares of PBs, including climate change and biogeochemical flows of nutrients. Traditional LCA (ReCiPe impact assessment) showed net savings for the H+ system in a few categories and considerable reductions in several impacts, e.g., global warming potential (GWP), stratospheric ozone depletion, terrestrial acidification, and water consumption. In PB-LCA the H+ system gave additional impacts in both assessments for a few categories, mostly due to high consumption of chemicals in the ammonium stripping process used for nutrient recovery. In conclusion, the combined assessments highlight hotspots for process optimization in the H+ system. From a methodological standpoint, PB-LCA still needs improvements to better reflect avoided burdens and results from traditional LCA should be fully transparent and analyzed carefully. The assessment methods complement each other and can be combined to better represent environmental performances of systems

Be circular – Från rötrester av svartvatten och köksavfall till flytande gödselmedel

Effektiv användning av ändliga resurser är ett av de främsta målen för en hållbar utveckling. I ett kretsloppsperspektiv skulle näringsrikt avloppsvatten och näring fastlagd i köksavfall kunna bli till flytande gödselmedel till hobbyodlare. Vår utgångspunkt var sidoströmmar från biogasproduktion, både svartvatten (d.v.s. toalettvatten) och den flytande fraktionen av köksavfall. I ett Partnerskap Alnarp projekt mellan SLU, AlnarpFoodTech Ek. för. och RecoLab vid NSVA i Helsingborg undersökte vi bland annat förbättringsområden för att ta fram en tillförlitlig och säker växtnäringsprodukt

Recycling – The future urban sink for wastewater and organic waste

The world’s population is estimated to reach 11 billion in this century, with some 8.5 billion living in urban areas. Cities become unprecedented hot spots of demand for virgin water and food, as well as producers of large volumes of valuable waste. The recycling of urban nutrient-rich liquid and solid waste as fertilizer in agriculture will thus be of benefit to both sectors. The analysis suggests that recycling has the potential to become the ultimate sink for organic waste and wastewater, while simultaneously securing the supply of food and fertilizers, and reducing both local and global environmental impacts. Presently, harmful chemical substances from various consumer products in our chemical society are disposed of in urban waste flows and hamper recovery and reuse. A combination of counter measures such as not mixing nutrient-rich blackwater with grey water polluted with chemical compounds, are crucial. The sludge from the small volume of blackwater can contribute enough fertilizers to secure global food supplies by the year 2100. The voluminous grey water will contain few pathogenic microorganisms and can be treated for non-potable reuse. Three urban arrangements are analysed: Singapore (entire city), Helsingborg in Sweden (city district), and Bangalore in India (eco-house)

Potential for nutrient recovery and biogas production from blackwater, food waste and greywater in urban source control systems.

In the last decades, the focus in waste and wastewater treatment systems has shifted towards increased recovery of energy and nutrients. Separation of urban food waste and domestic wastewaters using source control systems could aid this increase; however their effect on overall sustainability is unknown. To obtain indicators for sustainability assessments, five urban systems for collection, transport, treatment and nutrient recovery from blackwater, greywater and food waste were investigated using data from implementations in Sweden or northern Europe. The systems were evaluated against their potential for biogas production and nutrient recovery by the use of mass balances for organic material, nutrients and metals over the system components. The resulting indicators are presented in units suitable for use in future sustainability studies or life cycle assessment of urban waste and wastewater systems. The indicators show that source control systems have the potential to increase biogas production with more than 70% compared to a conventional system and give a high recovery of phosphorus and nitrogen as biofertilizer. The total potential increase in gross energy equivalence for source control systems was 20-100%; the greatest increase shown for vacuum-based systems

Management of hydrogen sulfide in anaerobic digestion of enzyme pretreated marine macro-algae

Enzymatic pretreatment of algae by means of cellulose degrading enzyme was evaluated through lab-scale and pilot-scale experiments. The degradation efficiency of the enzyme depended on the initial physical quality of the algae. Lab-scale batch anaerobic digestion experiments showed comparatively low methane potential for the pretreated algae at both mesophilic and thermophilic temperatures. However, the raw algae (cut into small pieces) were found to be hardly hydrolysable. The methane potential of raw algae in thermophilic and mesophilic digestion was about 17 NmL/g VS and –36 NmL/g VS respectively. Presence of inhibitory agent(s) was obvious at both temperatures. Very fast growth of sulfate-reducing bacteria was noticed in the continuous digestion, so that in less than 20 days, hydrogen sulfide concentrations over 10000 ppm were observed in both meso- and thermophilic reactors. Inhibition of methanogenesis in the thermophilic reactor occurred at unionized dissolved sulfide concentration of about 22 mg/L (10000 ppm in the biogas) while it was mainly non-SRB acetogens that were inhibited in the mesophilic reactor at unionized sulfide concentrations as high as 50 mg/L (17000 ppm in the biogas). This shows that probably thermophilic digestion is more prone to be inhibited at high sulfide concentrations. Micro-aeration was found to be more efficient in the thermophilic reactor while its effect on the mesophilic process was negligible