Resource recovery from wastewater and sludge: modelling and control challenges

Wastewater treatment plants (WWTPs) have been renamed water resource recovery facilities (WRRFs). Our industry is quickly moving from an end-of-pipe environmental protection service to an economic producer of valued products for society. Based on a critical review of resource recovery technologies that are currently applied or in advanced development, it became obvious that most of these technologies are based on physicochemical unit processes (precipitation, volatilization, sorption, …). Current industrial practice for the design and operation of WRRFs is based on mathematical models describing the traditional biological processes. The modeling challenge therefore is to provide practice with proper models for the physicochemical resource recovery processes. The fact that the WRRFs aim at delivering valued products that can partially replace those produced by other means (typically in the chemical industry) leads to a paradigm shift in specifications of the outputs of the facility: no longer treated wastewater and biosolids, but products that have to compete with what is already on the market. The tighter specifications will thus impose a challenge on the process control systems that will be required to guarantee the quality of the products of the WRRFs

Fate of micronutrients and heavy metals in digestate processing using vibrating reversed osmosis as resource recovery technology

This study aims to evaluate the full-scale performance of vibrating membrane filtration (VSEP) technology in resource recovery from the liquid fraction of digestates, while reducing macronutrient concentrations down to dischargeable water. Although increasing attention is paid to mass flow assessment of macronutrients, to date little is known about the fate of micronutrients and heavy metals upon digestate processing. In this research, process streams were characterized and mass balances for micronutrients and heavy metals were performed throughout a complete digestate processing train. The VSEP system operated with reversed osmosis membranes and followed by a lagoon was capable of producing dischargeable water according to Flemish regulatory standards. Concentrates produced by one VSEP filtration of the liquid fraction of digestate and dried thick fractions resulting from solid-liquid separation were rich in macro- and micronutrients, while heavy metal concentrations did not exceed regulatory standards. Hence, these products showed high potential for reuse in agriculture

Nutrient recycling from bio-digestion waste as green fertilizers

In the transition from a fossil to a bio-based economy, it has become an important challenge to maximally recuperate valuable nutrients coming from waste streams. Nutrient resources are rapidly depleting, significant amounts of fossil energy are used for the production of chemical fertilizers, whereas costs for energy and fertilizers are increasing. In the meantime, biogas production through anaerobic digestion produces nutrient-rich digestates. In high-nutrient regions, these products cannot or only sparingly be returned to agricultural land in its crude unprocessed form. The consequent processing of this digestate requires a variety of technologies producing a lot of different derivatives, which could potentially be re-used as green fertilizers in agriculture. As such, a sustainable alternative for fossil-based mineral fertilizers could be provided. The aim of this study is to characterize the physicochemical properties of digestates and derivatives, in order to identify the fertilizer value and potential bottlenecks for agricultural re-use of these products, in line with European legislative constraints. In addition, the economic and ecological benefits of substituting conventional fertilizers by digestates and derivatives are quantified and evaluated. Waste water from acidic air scrubbers for ammonia removal shows potential as N-S-fertilizer, whereas concentrates resulting from membrane filtrated liquid fraction of digestate show promise as N-K-fertilizer. Substituting artificial fertilizers by air scrubber water or membrane filtration concentrates theoretically always results in significant economic and ecological benefits for the agriculturist. Field research is now on-going in order to evaluate the impact on soil and crop production by application of these new green fertilizers

Nutrient recovery from bio-digestion waste: from field experimentation to model-based optimization

The increasing awareness of natural resource depletion, the increasing demand of nutrients and energy for food production, and the more and more stringent nutrient discharge and fertilization levels, have resulted in an increased attention for nutrient recovery from municipal and agricultural wastes. This PhD dissertation aims at stimulating the transition to a bio-based economy by providing (tools to develop) sustainable strategies for nutrient recovery from organic wastes following bio-energy production through anaerobic digestion (= bio-digestion waste). Particular attention is paid to the valorization of the recovered products as renewable substitutes for chemical fertilizers and/or as sustainable organo-mineral fertilizers in agriculture. Three complementary research phases were conducted: 1) technology inventory and product classification, 2) product value evaluation, 3) process modelling and optimization. In the first phase, a systematic technology review and product classification was performed. In phase 2, product characterizations and mass balance analyses at full-scale waste(water) resource recovery facilities (WRRFs) were executed. An economic and ecological evaluation of different bio-based fertilization scenarios was conducted and the most sustainable scenarios were selected for subsequent agronomic evaluation at field and greenhouse scale. In phase 3, a generic nutrient recovery model library was developed aiming at fertilizer quantity and quality as model outputs. Increased insights in unit process performance and interactions were obtained through global sensitivity analyses. The models were successfully used as a tool for treatment train configuration and optimization. Based on all acquired knowledge, a generic roadmap for setting up nutrient recovery strategies as function of fertilizer markets, legislations, and waste characterization was established. As such, the present dissertation further develops the concepts of maximally closing nutrient cycles in a cradle-to-cradle approach. The work reveals important evidence of the positive impact of recovered products on the economy, agronomy, and ecology of intensive plant production. Moreover, it provides the fundamental information and tools to facilitate the implementation and optimization of sustainable nutrient recovery strategies. All of this may open up new opportunities for sustainable and more bio-based economic growth and thus create a win-win situation for the environment, the society, and the economy in Belgium, Canada, and beyond

Nutrient recovery from digestates : techniques and end-products

In nitrate vulnerable zones application of animal manure to land is limited. Digestate from anaerobic digestion plants competes with manure for nutrient disposal on arable land, which forms a serious hinder for the biogas sector to develop in these regions. Hence, one of its biggest challenges is to find cost-effective and sustainable ways for digestate processing or disposal. Furthermore, primary phosphorus resources are becoming scarce and expensive and will be depleted within a certain time. This urges the need to recycle P from secondary sources, like digestate or manure. From a sustainability point of view, it seems therefore no more than logical that digestate processing techniques switched their focus to nutrient recovery rather than nutrient removal. This paper gives an overview of digestate processing techniques, with a special focus on nutrient recovery techniques. In this paper nutrient recovery techniques are delineated as techniques that (1) create an end-product with higher nutrient concentrations than the raw digestate or (2) separate the envisaged nutrients from organic compounds that are undesirable in the end-product, with the aim to produce an end-product that is fit for use in chemical or fertiliser industry or as a mineral fertiliser replacement. Various nutrient recovery techniques are described, with attention for some technical bottlenecks and the current state of development. Where possible, physicochemical characteristics of the endproducts are given

Nutrient recovery from biodigestion waste (water) streams and reuse as renewable fertilizers: a two-year field experiment

The aim of this study was to evaluate the impact of using bio-digestion waste derivatives as substitute for synthetic fertilizers and/or as P-poor equivalent for animal manure on soil and crop production. In a field trial, nutrient balances were assessed and the physicochemical soil fertility and quality were evaluated. The biogas yield of the harvested energy crops was also determined. An economical and ecological evaluation was conducted. The highest biomass yields were obtained when the liquid fraction of digestate was used as P-poor fertilizer in addition to animal manure. Furthermore, the complete substitution of synthetic fertilizer N by air scrubber waste water resulted in the highest N and P use efficiencies. Finally, for all reuse scenarios the calculated economical and ecological benefits were significantly higher as compared to the common practice using animal manure and synthetic fertilizers

Management of Nutrient-Rich Wastes and Wastewaters on Board of Ships

Ship-generated nutrient-rich waste sources, including food waste and sewage water, contribute to eutrophication and deoxygenation of marine ecosystems. This chapter aims to discuss the characteristics of these waste and wastewater sources, review current ship-generated organic waste and wastewater regulations, inventory conventional management and treatment practices, and identify future perspectives for more sustainable nutrient-rich waste and wastewater management on board of ships. According to regulations, untreated food waste and sewage can generally be discharged into the open sea at more than 12 nautical miles from the nearest land, hence this is currently a common practice. However, special restrictions apply in special designated areas such as the Baltic Sea, where food waste must be comminuted/grounded and nutrients need to be removed from the sewage prior to discharge at 12 nautical miles from the nearest land. Current research looks at the valorisation of these waste and wastewater sources through anaerobic digestion, composting and/or nutrient recovery