Fermentação de lodos ativados e resíduos orgânicos como co-substratos visando a solubilização de fósforo para otimizar a recuperação de estruvita

TCC(graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Engenharia Sanitária e Ambiental.O fósforo (P) é um elemento chave para a manutenção da vida. O P, porém, está sendo transferido rapidamente de reservas minerais para corpos hídricos, causando uma epidemia global de eutrofização de corpos d’água doce e zonas mortas oceânicas. Neste panorama, controlar a cristalização da estruvita, ou, magnésio amônio fosfato hexahidratado (MgNH4PO4.6H2O) é uma forma de obter um fertilizante agrícola com grandes vantagens sobre os fertilizantes minerais e, simultaneamente, de reduzir custos operacionais oriundos da formação espontânea deste cristal em estações de tratamento de esgoto (ETE). As taxas de eficiência na cristalização podem superar 90% de remoção do P dissolvido, porém as taxas de recuperação são muito inferiores quando relacionadas ao P total, visto que apenas uma fração encontra-se disponível (solubilizada). Logo, maximizar a solubilização do P contido no lodo é a etapa mais importante de sua recuperação. Esta pesquisa, realizada no Irstea - Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture, deu continuidade às pesquisas existente na área. O estudo visou otimizar o processo pela aplicação de uma abordagem inovadora: a aplicação de uma etapa de acidificação biológica através do uso de diferentes resíduos alimentares como co-substratos de digestão de lodo ativado em excesso. Os resíduos utilizados foram resíduos sólidos orgânicos urbanos, resíduos de restaurante coletivo, gordura de ETE, soro de leite, maçãs e cenouras. Foi possível simultaneamente favorecer a liberação de P pelas bactérias desfosfatantes e favorecer as formas solúveis de P em função dos baixos pH atingidos. Concentrações superiores a 250 mg.L-1 de P-PO4 3- foram atingidas, sendo que o limite de viabilidade para cristalização da estruvita está em torno de 50 mg.L-1. Foram avaliados métodos de separação do efluente rico em P solúvel e seus impactos na cristalização. Foram atingidas taxas de recuperação em torno de 50% do fósforo total

Anaerobic digestate˸ characterization and new valorization routes

Les post-traitements des digestats de méthanisation peuvent être inévitables, en particulier pour les exploitants d'installations non agricoles. Les options existantes pour la valorisation des digestats non-agricoles (NAD) sont limitées, souvent coûteuses et créent peu de valeur. L'objectif de cette thèse a été d'améliorer la valorisation des NAD via (i) une meilleure description et compréhension de la variabilité de la qualité des digestats et (ii) l'exploration de nouvelles voies de valorisation.Une typologie de la valeur fertilisante des digestats a été établie. Six types ont été différenciés en lien avec les intrants de méthanisation et le procédé (voie humide ou sèche). Les paramètres qui décrivent le mieux ces types sont la matière sèche du digestat, la teneur en azote et le rapport C/N. Ensuite, une méta-analyse a permis de mieux prédire la séparation de phase des digestats, une étape essentielle des configurations existantes. Ces deux études contribuent à mieux expliciter la variabilité de la qualité des digestats tant pour les scientifiques, les concepteurs et les opérateurs de méthaniseurs.Le «fractionnement» du digestat a été la principale approche expérimentale des voies innovantes explorées. La preuve de concept d'un procédé capable simultanément de stripper de l'azote et d'extraire des substances humique-like a été démontrée. Ces extraits ont été caractérisés et évalués en tant qu'amendements, biostimulants et biosurfactants. Enfin, l'approche de «conservation » a consisté en un séchage thermique direct du digestat brut, mais en privilégiant la fixation de l'azote. À cette fin, un acide et un adsorbant, comme améliorateurs de procédé, ont été appliqués avant le séchage. Seule l'acidification a permis de conserver l'azote et des limites expérimentales ont été discutées.L'exploration de nouvelles voies de valorisation des NAD a été fructueuse: des nouveaux concepts ont été testés et des perspectives positives proposées pour ouvrir des nouveaux marchés à partir de digestats. La valorisation efficace du digestat reste un défi, mais la thèse ouvre de nouvelles possibilités concrètes ainsi que de nouvelles questions scientifiques et techniques à explorer.Anaerobic digestate (AD) post-treatments can be unavoidable, especially for operators of non-agricultural AD facilities. Current options for the valorization of non-agricultural digestates (NAD) are limited, often costly and with low value creation. The objective of this thesis was to enhance NAD valorization routes through (i) better explaining digestate quality variability and (ii) assessing the potential of new recovery options for different types of digestates.A digestate fertilizing-value typology consisting of 6 different types was established. The types were linked to AD feedstock and process (wet or dry-AD). The typology was mainly described by digestate dry matter, nitrogen content and C/N ratio. After, a meta-analytic study allowed a better prediction of digestate phase separation efficiency, which is usually a key step on digestate valorization. These two studies clarify the variability of digestates for scientists, plant designers and operators.Digestate “fractioning” was the principal approach and the experimental focus of innovative digestate recovery. The proof-of-concept of a scalable process capable of stripping nitrogen and extracting humic-like substances was demonstrated. The extracts of humic-like substances were characterized and assessed as soil improvers, biostimulants and biosurfactants. Finally, the digestate “conservation” approach consisted of direct thermal drying of raw digestate but with a focus on keeping nitrogen. For this purpose, acidification and adsorbents, as a novelty process enhancer, were applied before drying. Only acidification was successful for N fixation under the tested conditions and experimental limits were highlighted.The exploration of innovative NAD valorization approaches was successful: new concepts were developed along with positive perspectives for entering new markets from digestates. Effective digestate valorization remains a challenge but the thesis opens new concrete possibilities, along with new scientific and technical questions to be investigate

A new strategy to increase phosphorus recovery yield from wastewater sludge

International audiencePhosphorus (P) recovery as struvite from wastewater activated sludge (WAS) is a developing technology usually applied to recycle dissolved P by adding magnesium (Mg) and increasing pH in the liquid effluent from the digestate dewatering step after anaerobic digestion (AD) of WAS. Consequently, the P recovery yield is depending on the dissolved P concentration in digestate which is usually only a small fraction of the P in WAS. The aim of this study was to increase the P recovery yield by favouring P dissolution by a biological way, not after but just before the AD of WAS as described in figure 1. Recovering P before AD is also a way to prevent struvite crystallization on pipes and equipment, reducing maintenance cost in AD plants. For that, acidogenesis was favoured by adding several different wastes as co-substrate in thickened WAS

Sequencing biological acidification of waste-activated sludge aiming to optimize phosphorus dissolution and recovery

Phosphorus (P) recovery in wastewater treatment plants (WWTP) as pure crystals such as struvite (MgNH4PO4.6H2O), potassium struvite (KMgPO4.6H2O) and calcium phosphates (e.g. Ca3(PO4)2) is an already feasible technique that permits the production of green and marketable fertilizers and the reduction of operational costs. Commercial crystallizers can recovery more than 90% of soluble P. However, most of the P in WWTP sludge is unavailable for the processes (not dissolved). P solubilization and separation are thus the limiting steps in P-crystallization. With an innovative two-step sequencing acidification strategy, the current study has aimed to improve biological P solubilization on waste-activated sludge (WAS) from a full-scale plant. In the first step (P-release), low charges of organic waste were used as co-substrates of WAS pre-fermentation, seeking to produce volatile fatty acids to feed the P-release by Polyphosphate-accumulating organisms, while keeping its optimal metabolic pH (6-7). In this phase, milk serum, WWTP grease, urban organic waste and collective restaurant waste were individually applied as co-substrates. In the second step (P-dissolution), pH 4 was aimed at as it allows the dissolution of the most common precipitated species of P. Biological acidification was performed by white sugar addition, as a carbohydrate-rich organic waste model, which was compared to chemical acidification by HCl (12M) addition. With short retention times (48-96 h) and without inoculum application, all experiences succeeded on P solubilization (37-55% of soluble P), principally when carbohydrate-rich co-substrates were applied. Concentrations from 270 to 450 mg were achieved

Typologie des digestats de méthanisation à partir de paramètres usuels de valeur amendement/fertilisante

Typologie des digestats de méthanisation à partir de paramètres usuels de valeur amendement/fertilisante. Journées Recherche et Industrie biogaz méthanisation - JRI 201

Biochar for enhancing anaerobic digestion of food waste

International audienc

Phosphorus recycling potential assessment by a biological test applied to wastewater sludge

Phosphorus (P) recycling as mineral fertilizer from wastewater activated sludge (WAS) depends on the amount that can be dissolved and separated from the organic matter before the final crystallization step. The aim of the biological phosphorus dissolution potential (BPDP) test developed here was to assess the maximum amount of P that could be biologically released from WAS prior that the liquid phase enters the recovery process. It was first developed for sludge combining enhanced biological phosphorus removal and iron chloride. Because carbohydrates are known to induce acidification during the first stage of anaerobic digestion, sucrose was used as a co-substrate. Best results were obtained after 24-48 h, without inoculum, with a sugar/sludge ratio of 0.5 gCOD/gVS and under strict anaerobic conditions. Up to 75% of the total phosphorus in sludge from a wastewater treatment plant combining enhanced biological phosphorus removal and iron chloride phosphorus removal could be dissolved. Finally, the test was applied to assess BPDP from different sludge using alum compounds for P removal. No dissolution was observed when alum polychloride was used and less than 20% when alum sulphate was used. In all the cases, comparison to chemical acidification showed that the biological process was a major contributor to P dissolution. The possibility to crystallize struvite was discussed from the composition of the liquids obtained. The BPDP will be used not only to assess the potential for phosphorus recycling from sludge, but also to study the influence of the co-substrates available for anaerobic digestion of sludge