Phosphorus recovery from domestic wastewater: A review of the institutional framework.

Phosphorus (P) is an essential element for life that must be managed sustainably. The institutional framework for P recovery from wastewater includes policies, regulations, plans, and actions that promote the recovery, recycling, and safe use of this element, aimed at moving toward more sustainable nutrient management and environmental protection. This review analyzes the status of the institutional framework for P recovery from wastewater in different countries around the world. Europe is the continent where the most progress has been made in terms of legislation. Countries such as Germany, the Netherlands, Austria, and Denmark have already implemented policies and regulations that promote environmental protection, as well as P recovery and reuse. In other parts of the world, such as the United States, China, and Japan, there have also been significant advances in promoting the closure of the P cycle, with the implementation of advanced recovery technologies in wastewater treatment plants and regional/national action plans. By contrast, in Latin America there has been little progress in P treatment and recovery, with a weak regulatory framework, unclear goals, and insufficient allocation of techno-economic resources. In this context, it is necessary to reinforce the comprehensive institutional framework, which covers technological aspects, economic incentives, political agreements, and regulations, to promote the sustainable management of this valuable resource.

Second-Generation Magnesium Phosphates as Water Extractant Agents in Forward Osmosis and Subsequent Use in Hydroponics.

The recovery of nutrients from wastewater streams for their later use in agricultural fertilization is an interesting approach. Wastewater recovered magnesium phosphate (MgP) salts were used in a forward osmosis (FO) system as draw solution in order to extract water and to produce a nutrient solution to be used in a hydroponic system with lettuces (Lactuca sativa, L.). Owing to the low solubility of the MgP salts (i.e., struvite, hazenite and cattiite) in water, acid dissolution was successfully tested using citric and nitric acids to reach pH 3.0. The dilution by FO of the dissolved salts reached levels close to those needed by a hydroponic culture. Ion migration through the membrane was medium to high, and although it did not limit the dilution potential of the system, it might decrease the overall feasibility of the FO process. Functional growth of the lettuces in the hydroponic system was achieved with the three MgP salts using the recovered water as nutrient solution, once properly supplemented with nutrients with the desired concentrations. This is an innovative approach for promoting water reuse in hydroponics that benefits from the use of precipitated MgP salts as a nutrient source.

Exploring the recovery of potassium-rich struvite after a nitrification-denitrification process in pig slurry treatment.

The integration of biological nitrogen (N) removal with struvite-type material recovery, which contained phosphorus (P) and potassium (K), was proved to be technically feasible in pig slurry treatment. Phosphate (PO4) salts were precipitated by raising the pH-value, using denitrified effluent and waste sludge purged from the bioreactor. When P was limiting, the unbalanced composition of the denitrified effluent resulted in low K-removal efficiency from the liquid phase; 10 % maximum when the initial pH-value was adjusted to 11.5 (93 % PO4-P recovery). By processing the waste sludge in two steps, using first ethylenediaminetetraacetic acid (EDTA) as an acidifier to release PO4 while preventing calcium interference, the K-removal efficiency reached 25 % (75 % PO4-P recovery). When K was limiting, the addition of newberyite particles resulted in the highest K-removal efficiency, up to 90 % (under online pH control to 10.5). Overall, new opportunities are envisaged for producing second-generation fertilizers potentially containing 0-1 % N, 11-17 % P and 6-8 % K.

Treatment of swine wastewater in continuous activated sludge systems under different dissolved oxygen conditions: Reactor operation and evaluation using modelling.

Swine wastewater was treated in two continuously aerated activated sludge (AS) systems at high (AS1: 1.7-2.6 mg/L) and low (AS2: 0.04-0.08 mg/L) dissolved oxygen (DO), and at three temperatures (10, 20, and 30 °C). Biochemical oxygen demand (BOD) removal was >94.8%. Meanwhile, total nitrogen (N) removal was significantly higher in AS2, at 64, 89, and 88%, than in AS1, at 12, 24, and 46%, for 10, 20, and 30 °C, respectively. The experimental data were considered in a simulation study using an AS model for BOD and N removal, which also included nitrite, free ammonia, free nitrous acid, and temperature. Simulations at high-DO showed that ammonium was partly oxidized into nitrate but not removed, whereas at low-DO ammonium was removed mainly through the nitrite shortcut in simultaneous nitrification-denitrification. This study demonstrates that treatment at low-DO is an effective method for removing N, and modelling a helpful tool for its optimization.

Nitrification of leachates from manure composting under field conditions and their use in horticulture.

This work aimed to demonstrate the feasibility of nitrification applied to the treatment of leachates formed during composting of cattle and pig manure in order to promote their further use as liquid fertilizer in horticulture. Nitrification trials were successfully conducted in summer and winter seasons under Mediterranean climate conditions. Subsequently, effect of using the nitrified effluents as nutritive solution in the fertigation of lettuce (Lactuca sativa L.) was assessed in terms of productivity and nutrient uptake. Similar productivities were obtained when using the nitrified effluents and a standard nutritive solution. However, results also evidenced high nutrient uptake, which indicates that dosage should be adjusted to culture requirements.

Assessment of a composting process for the treatment of beef cattle manure.

The intensive breeding of beef cattle in Juncosa de les Garrigues (Catalonia, Spain) leads to the production of a large volume of manure that needs appropriate management. Land application in the area at agronomic rates is not enough to ensure good management practices, making necessary extended on-farm storage and the export of part of the production to long distances. In this context, the implementation of a collective treatment based on composting could help in enhancing the handling of manure. We assessed a full-scale composting process based on turned windrows (W), and involving treatment of beef cattle manure (CM) alone (two typologies were considered according to carbon-to-nitrogen ratios of ~25 (CM1, W1) and ~14 (CM2, W2)), or mixed with bulking agent (CM2/BA, W3) and dewatered digested sewage sludge (CM2/BA/DDSS, W4). Composting significantly improved the transportability of nutrients (final volumes were 40-54% of the initial volume). Temperature >55°C was reached in all the treatments but following different time patterns. Under the applied conditions of turning and rewetting, 14 weeks of processing did not ensure the production of stable, and mature, compost. Thus, only compost from W1 attained the maximum degree of stability as well as concentration of ammonium-N < 0.01% (with ammonium-N/nitrate-N ratio of 0.2) and low phytotoxicity. However, high pH, salinity, and heavy metal contents (Cu and Zn) may limit its final use. Addition of BA was advised to be kept to minimum, whereas use of DDSS as a co-substrate was not recommended in agreement to the higher loss of N and levels of heavy metals in the final compost.

Estimation of parameter uncertainty for an activated sludge model using Bayesian inference: a comparison with the frequentist method.

The procedure commonly used for the assessment of the parameters included in activated sludge models (ASMs) relies on the estimation of their optimal value within a confidence region (i.e. frequentist inference). Once optimal values are estimated, parameter uncertainty is computed through the covariance matrix. However, alternative approaches based on the consideration of the model parameters as probability distributions (i.e. Bayesian inference), may be of interest. The aim of this work is to apply (and compare) both Bayesian and frequentist inference methods when assessing uncertainty for an ASM-type model, which considers intracellular storage and biomass growth, simultaneously. Practical identifiability was addressed exclusively considering respirometric profiles based on the oxygen uptake rate and with the aid of probabilistic global sensitivity analysis. Parameter uncertainty was thus estimated according to both the Bayesian and frequentist inferential procedures. Results were compared in order to evidence the strengths and weaknesses of both approaches. Since it was demonstrated that Bayesian inference could be reduced to a frequentist approach under particular hypotheses, the former can be considered as a more generalist methodology. Hence, the use of Bayesian inference is encouraged for tackling inferential issues in ASM environments.

Feasibility and interest of the anammox process as treatment alternative for anaerobic digester supernatants in manure processing--an overview.

Completely autotrophic nitrogen removal (ANR) is based on the combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox). It is a promising alternative for the subsequent treatment of biogas digester supernatants in livestock manure processing and nitrogen surplus scenarios. However, as no full-scale experiences in the treatment of manure digestates by ANR have been published to date, future field studies addressing treatment of this kind of effluent would be of great interest. Some topics to be considered in these studies would be coupling anaerobic digestion and ANR, analysis of the factors that affect the process, comparing reactor configurations, microbial ecology, gas emissions, and achieving robust performance. This paper provides an overview of published studies on ANR. Specific issues related to the applicability of the process for treating manure digestates are discussed. The energy requirements of ANR are compared with those of other technological alternatives aimed at recovering nitrogen from digester supernatants. The results of the assessment were shown to depend on the composition of the supernatant. In this regard, the PN-anammox process was shown to be more competitive than other alternatives particularly at concentrations of up to 2 kg NH4(+)-N m(-3).

Partial nitritation of swine wastewater in view of its coupling with the anammox process.

Partial nitritation (PN) of swine wastewater was investigated in a sequencing batch reactor (SBR) using a high-performance nitrifying sludge. Characteristics of the wastewater used were low content of biodegradable organic matter and a high alkalinity-to-ammonium ratio. The target oxidation of ammonium nitrogen (NH-N) to nitrite nitrogen (NO-N) was 57% (1.32 g NO-N g NH-N), which corresponds with the reaction ratio of the anaerobic ammonium oxidation (anammox). This target was successfully achieved at 32°C by controlling the inflow rate and the corresponding nitrogen loading rate (NLR). An average NLR of 1.47 g NH-N L d was applied to the partial nitritation sequencing batch reactor during a period of 70 d. The nitrite production rate obtained was 0.91 g NO-N L d. No nitrate was produced. The PN effluent contained 1.38 g NO-N g NH-N, which was within 5% of the target ratio. Under steady composition of the wastewater, the pH was shown to be a good indicator of the PN process performance. Furthermore, in a second sequencing batch reactor, the anaerobic ammonium oxidation process was effectively applied to the PN effluent, attaining a nitrogen conversion rate of 0.36 g N L d (14.3 mg N g volatile suspended solids h).

Anammox sludge immobilized in polyvinyl alcohol (PVA) cryogel carriers.

This study evaluated the use of PVA cryogels to encapsulate slow-growing anammox bacteria for deammonification treatment of wastewater. The cryogel pellets were prepared by freezing-thawing at -8 °C. On average, pellets contained 11.8 mg-TSS/g-pellet of enriched anammox sludge NRRL B-50286 (Candidatus Brocadia caroliniensis) in 4-mm cubes. They were tested with synthetic and partially nitrified swine wastewater using continuous stirred-tank reactors packed at 20% (w/v). The immobilized gel was retained inside the reactor by a screen that eliminated the need of sludge recycling. The stoichiometry of anammox reaction was maintained for more than 5 months under non-sterile conditions. The process was not limited by substrates availability unless quite low N concentration (<5 mg/L) achieving >93% removal efficiency. In mass balances, >80% of the potential N conversion activity was achieved (2920 mg-N/kg-pellet/d). In addition, the immobilized bacteria were resilient to inhibition at high nitrite concentrations (244-270 mg-N/L).

Manure treatment technologies: on-farm versus centralized strategies. NE Spain as case study.

Manure treatment has become an issue of concern in many farms in order to adequate their productions to the requirements of available arable lands. Such processing should be considered in the framework of a nutrient management planning (NMP) designed under local conditionals and considering cultivable soils as the end-users. In this context, decision on individual or collective scale should not be regarded as a main objective per se since such election should result from the NMP study and design. This paper is aimed to review existing experiences on manure treatment in NE Spain (Catalonia), either at farm or large scale. Some common factors identified in the successful experiences described are the involvement of farmers, technology suppliers and related authorities; energy and fertilizers prices; and the existence of a NMP as a global framework for actuations. Economical factors affecting decision about management and treatment scale are influenced by the density and the intensity of farming in a given area, which favour centralized NMPs and allow optimizing logistics.

An integrated biochemical and physical model for the composting process.

A dynamic model for the composting process has been developed, which integrates several biochemical and physical processes. Different microbial populations (mesophilic and thermophilic bacteria, actinomycetes and fungi) have been considered, each specialized in certain types of polymeric substrates (carbohydrates, proteins, lipids, hemicellulose, cellulose and lignin) and their hydrolysis products. Heat and mass transfer between the three phases of the system have been taken into account. The gas phase was considered to be composed by nitrogen, oxygen, carbon dioxide, ammonia and water vapour. Model computer simulations provided results that fitted satisfactory the experimental data. A sensitivity analysis was performed to determine the key parameters of the model. The partition of both the composting mass and the active biomass into different major groups of substrates and specialized microbial populations, as well as the factors affecting the gas-liquid equilibrium, were important for an accurate description of the composting process.