Biogas from mono- and co-digestion of microalgal biomass grown on piggery wastewater.

Biogas production has been suggested as a valid valorization solution for microalgal/bacteria biomass (MAB) grown on wastewater. This research is aimed at assessing the feasibility to use MAB grown in an outdoor raceway fed on piggery wastewater for biogas production. Batch and continuous anaerobic tests were conducted on the sole MAB and on a blend of MAB and carbonaceous substrates (deproteinated cheese whey and cellulose) to improve the carbon/nitrogen ratio. Results of batch biochemical methane potential tests confirmed that the sole microalgal/bacteria biomass was poorly degradable (119 NmLCH4·gCOD -1), while blending it with deproteinated cheese whey or cellulose (80% of carbonaceous material and 20% of MAB, as chemical oxygen demand (COD)) had no synergistic effects on the methane yield, although slight improvements in the degradation kinetics were observed. Continuous anaerobic degradation tests (at an organic loading rate of 1.5 gCOD·L-1·d-1, 35 °C and 30 days of hydraulic retention time) increased the overall methane yield from 81 NmLCH4·gCOD -1 (sole MAB) to 216 NmLCH4·gCOD -1 (MAB and deproteinated cheese whey) and 122 NmLCH4·gCOD -1 (MAB and cheese whey). However, data confirm that no evident synergistic effects were obtained.

Piggery wastewater treatment with algae-bacteria consortia: Pilot-scale validation and techno-economic evaluation at farm level.

The efficiency of an outdoor pilot-scale raceway pond treating the wastewaters generated by a large-scale piggery farm in Northern Italy was evaluated. The biomass productivity over 208 days of experimentation was 10.7 ± 6.5 g TSS·m-2·d-1, and ammoniacal nitrogen, orthophosphate, and COD average removal efficiencies were 90%, 90%, and 59%, respectively. Results were used to perform a comprehensive techno-economic analysis for integrating algae-based processes in farms of different sizes (100-10000 pigs). The amount of N disposed of on agricultural land could be reduced from 91% to 21%, increasing the fraction returned to the atmosphere from 2.4% to 63%, and the fraction in the biomass from 6.2% to 16%. For intensive farming, the release of 110 t N·ha-1·y-1 contained in the digestate could be avoided by including algae-bacteria processes. The biomass production cost was as low as 1.9 €·kg-1, while the cost for nitrogen removal was 4.3 €·kg N-1.

Metal-based flocculation to harvest microalgae: a look beyond separation efficiency.

Metal-based flocculants are commonly used for biomass harvesting in microalgae-based bio-refineries. Besides the high separation efficiency, additional aspects should be considered, related to the toxicity of metals for the algal biomass. Partitioning tests for commonly used flocculants (i.e., FeCl3 and Al2(SO4)3) showed that metals were mostly transferred to the solid phase with more than 95% of dosed metal ending up into the biomass, and low metal concentrations in the liquid effluent (lower than 0.4 mg L-1 for both metals), thus allowing for water reuse. Photosynthesis inhibition was tested on microalgae and microalgae-bacteria cultures, using a standardized photo-respirometry protocol in which typical concentrations used during coagulation-flocculation were assessed. Modelling dose-response curves, concentrations corresponding to 50% inhibition (IC50) were obtained, describing short-term effects. The obtained IC50 ranged from 13.7 to 28.3 mg Al L-1 for Al, and from 127.9 to 195.8 mg Fe L-1 for Fe, showing a higher toxicity for the Al-based flocculant. The recovery of photosynthesis inhibition was also quantified, to evaluate the possibility of reusing/recycling the harvested biomass. The results highlighted that the residual photosynthetic activities, evaluated after 1 h and 24 h of exposure to metals were partially recovered, especially for Al, passing from 67.3% to 94.6% activity, respectively, while long-term Fe effects were stronger (passing from 64.9% to 77.6% activity). A non-toxic flocculant (cationic starch) was finally tested, excluding potential effects due to biomass aggregation, as the reduction of photosynthetic activity only reached 3.4%, compared to control. Relevant modifications to the light availability and the optical properties of algal suspensions were assessed, identifying a strong effect of iron which caused an increase of the light absorbance up to approximately 40% at high Fe concentrations. Possible implications of dosing metallic flocculants in MBWWT processes are discussed, and suggestions are given to perform inhibition tests on flocculating chemicals.

Digestate treatment with algae-bacteria consortia: A field pilot-scale experimentation in a sub-optimal climate area.

This paper addresses the efficiency of a microalgae-based agricultural digestate treatment at pilot-scale in an outdoor raceway pond (880 L, pH-dependent CO2 dosage) and in a bubble column (74.5 L, air-bubbling). Specifically, nitrogen removal, evolution of the algae-bacteria consortium, and the actual process applicability in the Po Valley climate are discussed. The performance of the two reactors varied seasonally. The average algal productivity in the raceway was 32.4 ±â€¯33.1 mg TSS·L-1·d-1 (8.2 ±â€¯8.5 g TSS·m-2·d-1) while in the PBR it was 25.6 ±â€¯26.8 mg TSS·L-1·d-1; the average nitrogen removal was 20 ±â€¯29% (maximum 78%) and 22 ±â€¯29% (maximum 71%) in the raceway and in the column, respectively. Nevertheless, nitrification had a key role as 61 ±â€¯24% and 52 ±â€¯32% of the nitrogen load was oxidized in the raceway and in the column, respectively.

Sex ratio determination in bovine semen: a new approach by quantitative real time PCR.

Sex preselection of livestock offspring in cattle represents, nowadays, a big potential for genetic improvement and market demand satisfaction. Sperm sorting by flow cytometer provides a powerful tool for artificial insemination and production of predefined sexed embryos but, an accurate verification of the yield of sperm separation remains essential for a field application of this technique or for improvement and validation of other related semen sexing technologies. In this work a new method for the determination of the proportion of X- and Y-bearing spermatozoa in bovine semen sample was developed by real time PCR. Two sets of primers and internal TaqMan probes were designed on specific X- and Y-chromosome genes. To allow a direct quantification, a standard reference was established using two plasmid cDNA clones (ratio 1:1) for the specific gene targets. The method was validated by a series of accuracy, repeatability and reproducibility assays and by testing two sets of sorted and unsorted semen samples. A high degree of accuracy (98.9%), repeatability (CV=2.58%) and reproducibility (CV=2.57%) was shown. The results of X- and Y-sorted semen samples analysed by real time PCR and by flow cytometric reanalysis showed no significant difference (P>0.05). The evaluation of X-chromosome bearing sperms content in unsorted samples showed an average of 51.11+/-0.56% for ejaculates and 50.17+/-0.58% for the commercial semen. This new method for quantification of the sexual chromosome content in spermatozoa demonstrated to be rapid and reliable, providing a valid support to the sperm sexing technologies.

Comparison between primary sex ratio in spermatozoa of bulls and secondary sex ratio in the deriving offspring.

The objectives of the present work were to compare the primary sex ratio in sperm with the secondary sex ratio recorded in the offspring produced by artificial insemination (AI) with the same sperm and assess whether the primary sex ratio is influenced by sperm survival and motility after thawing. Calving data of 98 Holstein Friesian bulls used in AI were collected during 4 years, and commercial semen of the same bulls was analyzed immediately after thawing and after swim-up using a real-time polymerase chain reaction method developed and validated in our laboratory. Calving data relative to single bulls did not reveal any significant deviation between genders from the theoretical 1:1 for none of the bulls, being the mean values of male and female calves born 52.1 ± 2.80% and 47.9 ± 2.71%, respectively. Thereafter, calving events of bulls were classified and analyzed according to four classes of years: 2009 (n = 13,261), 2010 (n = 21,551), 2011 (n = 24,218), and 2012 (n = 41,726), and seasons categorized as winter, spring, summer, and fall. When data aggregated per years were analyzed, the difference between the two sexes was significant (P < 0.005) in favor of the male gender, whereas no influence of the season was evidenced. Real-time polymerase chain reaction did not evidence any difference between the mean values of frequency of Y chromosome-bearing sperm detected in three sperm batches of the same bulls analyzed immediately after thawing (51.1 ± 2.1), nor a difference with respect to the theoretical 1:1 ratio was reported after sperm analysis of one batch of sperm of the bulls analyzed after swim-up and immediately after thawing (50.1 ± 2.1 and 49.8 ± 1.8, respectively). The results are consistent with the observation of the farmers who often report a skewed sex ratio of the calves being born with AI in favor of the male gender. However, we have not evidenced differences in the primary sex ratio with respect to the theoretical 1:1 ratio both at thawing and after swim-up, thus demonstrating that the freezing procedure itself does not impact selectively on the survival of the X or Y chromosome-bearing sperm. Therefore, we hypothesize that the difference between genders observed after AI is more likely due to the events occurring after fertilization, which can comprise an impaired function of the X- or Y-bearing sperm with consequences on embryo development or a maternal influence.